U.S. Government Printing Office Style Manual/Capitalization Rules

3.1.
It is impossible to give rules that will cover every conceivable problem in capitalization; but by considering the purpose to be served and the underlying principles, it is possible to attain a considerable degree of uniformity. The list of approved forms given in Chapter 4 will serve as a guide. Obviously such a list cannot be complete. The correct usage with respect to any term not included can be determined by analogy or by application of the rules.
Proper names
3.2.

Proper names are capitalized.

Rome
Brussels
John Macadam
Macadam family
Italy
Anglo-Saxon
Derivatives of proper names
3.3.

Derivatives of proper names used with a proper meaning are capitalized.

Roman (of Rome)
Johannean
Italian
3.4.

Derivatives of proper names used with acquired independent common meaning, or no longer identified with such names, are set lowercased. Since this depends upon general and long-continued usage, a more definite and all-inclusive rule cannot be formulated in advance.

roman (type)
brussels sprouts
venetian blinds
macadam (crushed rock)
watt (electric unit)
plaster of pairs
italicize
anglicize
pasteurize
Common nouns and adjectives in proper names
3.5.
A common noun or adjective forming an essential part of a proper name is capitalized; the common noun used alone as a substitute for the name of a place or thing is not capitalized.
Massachusetts Avenue; the avenue
Washington Monument; the monument
Statue of Liberty; the statue
Hoover Dam; the dam
Boston Light; the light
Modoc National Forest; the national forest
Panama Canal; the canal
Soldiers' Home in Holyoke; the soldiers' home
Johnson House (hotel); Johnson house (residence)
Crow Reservation; the reservation
Cape of Good Hope; the cape
Jersey City
Washington City

but city of Washington; the city

Cook County; the county
Great Lakes; the lakes
Lake of the Woods; the lake
North Platte River; the river
Lower California

but lower Mississippi

Charles the First; Charles I
Seventeenth Census; the 1960 census
3.6.

If a common noun or adjective forming an essential part of a name becomes separated from the rest of the name by an intervening common noun or adjective, the entire expression is no longer a proper noun and is therefore not capitalized.

Union Station: union passenger station
Eastern States: eastern farming States
United States popularly elected government
3.7.

A common noun used alone as a well-known short form of a specific proper name is capitalized.

the Capitol building in Washington, DC; but State capital building
the Channel (English Channel)
the Chunnel (tunnel below English Channel)
the District (District of Columbia)
3.8.

The plural form of a common noun capitalized as part of a proper name is also capitalized.

Seventh and I Streets
Lakes Erie and Ontario
Potomac and James Rivers
State and Treasury Departments
British, French, and United States Governments
Presidents Washington and Adams
3.9.
A common noun used with a date, number, or letter, merely to denote time or sequence, or for the purpose of reference, record, or temporary convenience, does not form a proper name and is therefore not capitalized. (See also rule 3.38.)
abstract B
act of 1928
amendment 5
apartment 2
appendix C
article I
book II
chapter III
chart B
class I
collection 6
column 2
drawing 6
exhibit D
figure 7
first district (not congressional)
flight 007
graph 8
group 7
history 301
mile 7.5
page 2
paragraph 4
part I
phase 3
plate IV
region 3
room A722
rule 8
schedule K
section 3
signature 4
spring 1926
station 27
table 4
title IV
treaty of 1919
volume X
war of 1914
ward 2
3.10.

The following terms are lowercased, even with a name or number

aqueduct
irrigation project
shipway
breakwater
jetty
slip
buoy
levee
spillway
chute
lock
turnpike
dike
pier
watershed
dock
reclamation project
weir
drydock
ship canal
wharf
Definite article in proper place names
3.11.

To achieve greater distinction or to adhere to the authorized form, the word the (or its equivalent in a foreign language) is capitalized when used as a part of an official name or title. When such name or title is used adjectively, the is not capitalized, nor is the supplied at any time when not in copy.

British Consul v. The Mermaid (title of legal case)
The Dalles (OR); The Weirs (NH); but the Dalles region; the Weirs streets
The Hague; but the Hague Court; the Second Hague Conference
El Salvador; Las Cruces; L'Esterel
The National Mall; The Mall (Washington, DC only)
The Gambia but the Congo, the Sudan, the Netherlands
3.12.

In common practice, rule 3.11 is disregarded in references to newspapers, periodicals, vessels, airships, trains, firm names, etc.

the Washington Post
the Times
the Atlantic Monthly
the Mermaid
the U-3
the Los Angeles
the Federal Express
the National Photo Co.
Particles in names of persons
3.13.

In foreign names such particles as d', da, de, della, den, du, van, and von are capitalized unless preceded by a forename or title. Individual usage, if ascertainable, should be followed.

Da Ponte; Cardinal da Ponte
Den Uyl; Johannes den Uyl; Prime Minister den Uyl
Du Pont; E.I. du Pont de Nemours & Co.
Van Rensselaer; Stephen van Rensselaer
Von Braun; Dr. Wernher von Braun

but d'Orhigny; Alcide d'Orbigny; de la Madrid; Miguel de la Madrid

3.14.

In anglicized names such particles are usually capitalized, even if preceded by a forename or title, but individual usage, if ascertainable, should be followed.

Justice Van Devanter; Reginald De Koven
Thomas De Quincey; William De Morgan
Henry van Dyke (his usage)
Samuel F. Du Pont (his usage); Irénée du Pont
3.15.

If copy is not clear as to the form of such a name (for example, La Forge or Laforge), the two-word form should be used.

De Kalb County (AL, GA, IL, IN)

but DeKalb County (TN)

3.16.

In names set in capitals, de, von, etc., are also capitalized.

Names of organized bodies
3.17.

The full names of existing or proposed organized bodies and their shortened names are capitalized; other substitutes, which are most often regarded as common nouns, are capitalized only in certain specified instances to indicate preeminence or distinction.

National governmental units:

U.S. Congress: 110th Congress; the Congress; Congress; the Senate; the House; Committee of the Whole, the Committee; but committee (all other congressional committees)
Department of Agriculture: the Department; Division of Publications, the Division; similarly all major departmental units; but legislative, executive, and judicial departments
Bureau of the Census: the Census Bureau, the Bureau; but the agency
Environmental Protection Agency: the Agency
Geological Survey: the Survey
Government Printing Office: the Printing Office, the Office
American Embassy, British Embassy: the Embassy; but the consulate; the consulate general
Treasury of the United States: General Treasury; National Treasury; Public Treasury; the Treasury; Treasury notes; New York Subtreasury, the subtreasury
Department of Defense: Military Establishment; Armed Forces; All-Volunteer Forces; but armed services
U.S. Army: the Army; All-Volunteer Army; the Infantry; 81st Regiment; Army Establishment; the Army Band; Army officer; Regular Army officer; Reserve officer; Volunteer officer; but army shoe; Grant's army; Robinson's brigade; the brigade; the corps; the regiment; infantryman
U.S. Navy: the Navy; the Marine Corps; Navy (Naval) Establishment; Navy officer; but naval shipyard; naval officer; naval station
U.S. Air Force: the Air Force
U.S. Coast Guard: the Coast Guard
French Ministry of Foreign Affairs; the Ministry; French Army; British Navy

International organizations:

United Nations: the Council; the Assembly; the Secretariat
Permanent Court of Arbitration: the Court; the Tribunal (only in the proceedings of a specific arbitration tribunal)
Hague Peace Conference of 1907: the Hague Conference; the Peace Conference; the Conference

Common-noun substitutes:

Virginia General Assembly: the assembly
California State Highway Commission: Highway Commission of California; the highway commission; the commission
Montgomery County Board of Health: the Board of Health, Montgomery County; the board of health; the board
Common Council of the City of Pittsburgh: the common council; the council
Buffalo Consumers' League: the consumers' league; the league
Republican Party: the party
Southern Railroad Co.: the Southern Railroad; Southern Co.; Southern Road; the railroad company; the company
Riggs National Bank: the Riggs Bank; the bank
Metropolitan Club: the club
Yale School of Law: Yale University School of Law; School of Law, Yale University; school of law
3.18.

The names of members and adherents of organized bodies are capitalized to distinguish them from the same words used merely in a descriptive sense.

a Representative (U.S.)
a Republican
an Elk
a Federalist
a Shriner
a Socialist
an Odd Fellow
a Communist
a Boy Scout
a Knight (K.C, K.R, etc.)
Names of countries, domains, and administrative divisions
3.19.

The official designations of countries, national domains, and their principal administrative divisions are capitalized only if used as part of proper names, as proper names, or as proper adjectives. (See Chapter 17, Principal Foreign Countries table.)

United States: the Republic; the Nation; the Union; the Government; also Federal, Federal Government; but republic (when not referring specifically to one such entity); republican (in general sense); a nation devoted to peace
New York State: the State, a State (a definite political subdivision of first rank); State of Veracruz; Balkan States; six States of Australia; State rights; but state (referring to a federal government, the body politic); foreign states; church and state; statehood; state's evidence
Territory (Canada): Yukon, Northwest Territories; the Territory(ies), Territorial; but territory of American Samoa, Guam, Virgin Islands
Dominion of Canada: the Dominion; but dominion (in general sense) Ontario Province, Province of Ontario: the Province, Provincial; but province, provincial (in general sense)
3.20.
The similar designations commonwealth, confederation (federal), government, nation (national), powers, republic, etc., are capitalized only if used as part of proper names, as proper names, or as proper adjectives.
British Commonwealth, Commonwealth of Virginia: the Commonwealth; but a commonwealth government (general sense)
Swiss Confederation: the Confederation; the Federal Council; the Federal Government; but confederation, federal (in general sense)
French Government: the Government; French and Italian Governments: the Governments; but government (in general sense); the Churchill government; European governments
Cherokee Nation: the nation; but Greek nation; American nations
National Government (of any specific nation); but national customs
Allied Powers, Allies (in World Wars I and II); but our allies, weaker allies; Central Powers (in World War I); but the powers; European powers
Republic of South Africa: the Republic; but republic (in general sense)
Names of regions, localities, and geographic features
3.21.

A descriptive term used to denote a definite region, locality, or geographic feature is a proper name and is therefore capitalized; also for temporary distinction a coined name of a region is capitalized.

the North Atlantic States
the Gulf States
the Central States
the Pacific Coast States
the Lake States
East North Central States
Eastern North Central States
Far Western States
Eastern United States
the West
the Midwest
the Middle West
the Far West
the Eastern Shore (Chesapeake Bay)
the Badlands (SD and NE)
the Continental Divide
Deep South
Midsouth
the Far East
Far Eastern
the East
Middle East
Middle Eastern
Mideast
Mideastern (Asia)
Near East (Balkans, etc.)
the Promised Land
the Continent (continental Europe)
the Western Hemisphere
the North Pole
the North and South Poles
the Temperate Zone
the Torrid Zone
the East Side
Lower East Side (sections of a city)
Western Europe, Central Europe (political entities)

but
lower 48 (States)
the Northeast corridor
3.22.
A descriptive term used to denote mere direction or position is not a proper name and is therefore not capitalized.
north; south; east; west
northerly; northern; northward
eastern; oriental; occidental

east Pennsylvania
southern California
northern Virginia
west Florida; but West Florida (1763-1819)
eastern region; western region
north-central region
east coast; eastern seaboard
northern Italy
southern France

but East Germany; West Germany (former political entities)

Names of calendar divisions
3.23.

The names of calendar divisions are capitalized.

January; February; March; etc.
Monday; Tuesday; Wednesday; etc.

but spring; summer; autumn (fall); winter

Names of holidays, etc.
3.24.

The names of holidays and ecclesiastic feast and fast days are capitalized.

April Fools' Day
Arbor Day
Armed Forces Day
Birthday of Martin Luther King, Jr.
Christmas Day, Eve
Columbus Day
Father's Day
Feast of the Passover; the Passover
Flag Day Rosh Hashanah
Fourth of July; the Fourth
Halloween
Hanukkah
Hogmanay
Inauguration Day (Federal)
Independence Day
Labor Day
Lincoln's Birthday
Memorial Day (also Decoration Day)
Mother's Day
New Year's Day, Eve
Presidents Day
Ramadan
St. Valentine's Day
Thanksgiving Day
Washington's Birthday
Yom Kippur

but election day, primary day

Trade names and trademarks
3.25.

Trade names, variety names, and names of market grades and brands are capitalized. Some trade names have come into usage as generic terms (e.g., cellophane, thermos, and aspirin); when reference is being made to the formal company or specific product name, capitalization should be used. (See Chapter 4 "Capitalization Examples" trade names and trademarks.)

Choice lamb (market grade)
Red Radiance rose (variety)
Xerox (the company)

but photocopy (the process)

Scientific names
3.26.

The name of a phylum, class, order, family, or genus is capitalized. The name of a species is not capitalized, even though derived from a proper name. (See rule 11.9.)

Arthropoda (phylum), Crustacea (class), Hypoparia (order), Agnostidae (family), Agnostus (genus)
Agnostus canadensis; Aconitum wilsoni; Epigaea repens (genus and species)
3.27.

In scientific descriptions coined terms derived from proper names are not capitalized.

aviculoid
menodontine
3.28.

Any plural formed by adding s to a Latin generic name is capitalized.

Rhynchonellas
Spirifers
3.29.

In soil science the 12 soil orders are capitalized. (See Chapter 4 "Capitalization Examples" soil orders.)

Alfisols
Andisols
Aridisols
3.30.

Capitalize the names of the celestial bodies as well as the planets.

Sun
Earth
Venus
Moon
Mercury
Mars
Jupiter
Uranus
Saturn
Neptune

but the moons of Jupiter

Historical or political events
3.31.

Names of historical or political events used as a proper name are capitalized.

Battle of Bunker Hill
Christian Era
D-day
Dust Bowl
Fall of Rome
Great Depression
Great Society
Holocaust, the
Middle Ages
New Deal
New Federalism
New Frontier
Prohibition
Restoration, the
Reformation
Renaissance
Revolution, the
American, 1775
English, 1688
French, 1789
Russian, 1917
V-E Day
War of 1812
War on Poverty

but Korean war; cold war; Vietnam war; gulf war

Personification
3.32.

A vivid personification is capitalized.

The Chair recognizes the gentlewoman from New York;

but I spoke with the chair yesterday.

For Nature wields her scepter mercilessly.
All are architects of Fate,
Working in these walls of Time.
Religious terms
3.33.

Words denoting the Deity except who, whose, and whom; names for the Bible and other sacred writings and their parts; names of confessions of faith and of religious bodies and their adherents; and words specifically denoting Satan are all capitalized.

Heavenly Father; the Almighty; Lord; Thee; Thou; He; Him; but himself; You, Your; Thy, Thine; [God's] fatherhood
Mass; red Mass; Communion
Divine Father; but divine providence; divine guidance; divine service
Son of Man; Jesus' sonship; the Messiah; but a messiah; messiahship; messianic; messianize; christology; christological
Bible, Holy Scriptures, Scriptures, Word; Koran; also Biblical; Scriptural; Koranic
New Testament; Ten Commandments
Gospel (memoir of Christ); but gospel music
Apostles' Creed; Augsburg Confession; Thirty-nine Articles
Episcopal Church; an Episcopalian; Catholicism; a Protestant
Christian; also Christendom; Christianity; Christianize
Black Friars; Brother(s); King's Daughters; Daughter(s); Ursuline Sisters; Sister(s)
Satan; the Devil; but a devil; the devils; devil's advocate
Titles of persons
3.34.

Civil, religious, military, and professional titles, as well as those of nobility, immediately preceding a name are capitalized.

President Bush
Queen Elizabeth II
Ambassador Acton
Lieutenant Fowler
Chairman Williams
Dr. Bellinger
Nurse Joyce Norton
Professor Leverett
Examiner Jones (law)
Vice-Presidential candidate Smith

but baseball player Ripken; maintenance man Flow; foreman Collins

3.35.

To indicate preeminence or distinction in certain specified instances, a common-noun title immediately following the name of a person or used alone as a substitute for it is capitalized.

Title of a head or assistant head of state:

George W. Bush, President of the United States: the President; the President-elect; the Executive; the Chief Magistrate; the Commander in Chief; ex-President Clinton; former President Truman; similarly the Vice President; the Vice-President-elect; ex-Vice-President Gore
Tim Kaine, Governor of Virginia: the Governor of Virginia; the Governor; similarly the Lieutenant Governor; but secretary of state of Idaho; attorney general of Maine

Title of a head or assistant head of an existing or a proposed National governmental unit:

Condoleezza Rice, Secretary of State: the Secretary; similarly the Acting Secretary; the Under Secretary; the Assistant Secretary; the Director; the Chief or Assistant Chief; the Chief Clerk; but Secretaries of the military departments; secretaryship

Titles of the military:

General of the Army(ies): United States only; Supreme Allied Commander; Admiral Michael Mullen, Chairman, Joint Chiefs of Staff; Joint Chiefs of Staff; Chief of Staff, U.S. Air Force; the Chief of Staff; but the commanding general; general (military title standing alone not capitalized)

Titles of members of diplomatic corps:

Walter S. Gifford, Ambassador Extraordinary and Plenipotentiary: the American Ambassador; the British Ambassador; the Ambassador; the Senior Ambassador; His Excellency; similarly the Envoy Extraordinary and Minister Plenipotentiary; the Envoy; the Minister; the Chargé d'Affaires; the Charge; Ambassador at Large; Minister Without Portfolio; but the consul general; the consul; the attaché

Title of a ruler or prince:

Elizabeth II, Queen of England: the Queen; the Crown; Her Most Gracious Majesty; Her Majesty; similarly the Emperor; the Sultan
Charles, Prince of Wales: the Prince; His Royal Highness

Titles not capitalized:

Charles F. Hughes, rear admiral, U.S. Navy: the rear admiral
Steven Knapp, president of The George Washington University: the president
C.H. Eckles, professor of dairy husbandry: the professor
Barbara Prophet, chairwoman of the committee; the chairman; the chairperson; the chair
3.36.

In formal lists of delegates and representatives of governments, all titles and descriptive designations immediately following the names should be capitalized if any one is capitalized.

3.37.

A title in the second person is capitalized.

Your Excellency
Your Highness
Your Honor
Mr. Chairman
Madam Chairman
Mr. Secretary

but not salutations:

my dear General
my dear sir
Titles of publications, papers, documents, acts, laws, etc.
3.38.

In the full or short English titles of periodicals, series of publications, annual reports, historic documents, and works of art, the first word and all important words are capitalized.

Statutes at Large; Revised Statutes; District Code; Bancroft's :History; Journal (House or Senate) (short titles); but the code; the statutes
Atlantic Charter; Balfour Declaration; but British white paper
Chicago's American; but Chicago American Publishing Co.
Reader's Digest; but New York Times Magazine; Newsweek magazine
Monograph 55; Research Paper 123; Bulletin 420; Circular A; Article 15: Uniform Code of Military Justice; Senate Document 70; House :Resolution 45; Presidential Proclamation No. 24; Executive Order No. 24; Royal Decree No. 24; Public Law 89-1; Private and Union Calendars; Calendar No. 80; Calendar Wednesday; Committee Print No. 32, committee print; but Senate bill 416; House bill 61; Congressional Record
Annual Report of the Public Printer, 2007; but seventh annual report, 19th annual report
Declaration of Independence; the Declaration
Constitution (United States or with name of country); constitutional; but New York State constitution: first amendment, 12th amendment
Kellogg Pact; North Atlantic Pact; Atlantic Pact; Treaty of Versailles; Jay Treaty; but treaty of peace, the treaty (descriptive designations); treaty of 1919
United States v. Four Hundred Twenty-two Casks of Wine (law)
American Gothic, Nighthawks (paintings)
3.39.
All principal words are capitalized in titles of addresses, articles, books, captions, chapter and part headings, editorials, essays, headings, headlines, motion pictures and plays (including television and radio programs), papers, short poems, reports, songs, subheadings, subjects, and themes. The foregoing are also quoted.
3.40.

In the short or popular titles of acts (Federal, State, or foreign) the first word and all important words are capitalized.

Revenue Act; Walsh-Healey Act; Freedom of Information Act; Classification Act; but the act; Harrison narcotic law; Harrison narcotic bill; interstate commerce law; sunset law
3.41.

The capitalization of the titles of books, etc., written in a foreign language is to conform to the national practice in that language.

First words
3.42.

The first word of a sentence, of an independent clause or phrase, of a direct quotation, of a formally introduced series of items or phrases following a comma or colon, or of a line of poetry, is capitalized.

The question is, Shall the bill pass?
He asked, "And where are you going?"
The vote was as follows: In the affirmative, 23; in the negative, 11; not voting, 3.
Lives of great men all remind us
We can make our lives sublime.
3.43.

The first word of a fragmentary quotation is not capitalized.

She objected "to the phraseology, not to the ideas."
3.44.

The first word following a colon, an exclamation point, or a question mark is not capitalized if the matter following is merely a supplementary remark making the meaning clearer.

Revolutions are not made: they come.
Intelligence is not replaced by mechanism: even the televox must be guided by its master's voice.
But two months dead! nay, not so much; not two.
What is this? Your knees to me? to your corrected son?
3.45.

The first word following Whereas in resolutions, contracts, etc., is not capitalized; the first word following an enacting or resolving clause is capitalized.

Whereas the Constitution provides * * *; and
Whereas, moreover, * * *: Therefore be it
Whereas the Senate provided for the * * *: Now, therefore, be it
Resolved, That * * *; and be it further
Resolved (jointly), That * * *
Resolved by the House of Representatives (the Senate concurring), That * * *. (Concurrent resolution, Federal Government.)
Resolved by the Senate of Oklahoma (the House of Representatives concurring therein), That * * *, (Concurrent resolution, using name of State.)
Resolved by the senate (the house of representatives concurring therein), That * * *. (Concurrent resolution, not using name of State.)
Resolved by the Assembly and Senate of the State of California (jointly), That * * *. (Joint resolution, using name of State.)
Resolved by the Washington Board of Trade, That * * *
Provided, That * * *
Provided further, That * * *
Provided, however, That * * *
And provided further, That * * *
Ordered, That * * *
Be it enacted, That * * *
Center and side heads
3.46.

Unless otherwise marked, centerheads are set in capitals, and sideheads are set in lowercase and only the first word and proper names are capitalized. In centerheads making two lines, wordbreaks should be avoided. The first line should be centered and set as full as possible.

3.47.

In heads set in caps, a small-cap c or ac, if available, is used in such names as McLean or MacLeod; otherwise a lowercase c or ac is used. In heads set in small caps, a thin space is used after the c or the ac.

3.48.

In such names as LeRoy, DeHostis, LaFollette, etc. (one-word forms only), set in caps, the second letter of the particle is made a small cap, if available; otherwise lowercase is used. In heads set in small caps, a thin space is used. (See rule 3.15.)

3.49.
In matter set in caps and small caps or caps and lowercase, capitalize all principal words, including parts of compounds which would be capitalized standing alone. The articles a, an, and the; the prepositions at, by, for, in, of, on, to, and up; the conjunctions and, as, but, if, or, and nor; and the second element of a compound numeral are not capitalized. (See also rule 8.129.)
World en Route to All-Out War
Curfew To Be Set for 10 o'Clock
Man Hit With 2-Inch Pipe
No-Par-Value Stock for Sale
Yankees May Be Winners in Zig-Zag Race
Ex-Senator Is To Be Admitted
Notice of Filing and Order on Exemption From Requirements
but Building on Twenty-first Street (if spelled)
One Hundred Twenty-three Years (if spelled)
Only One-tenth of Shipping Was Idle
Many 35-Millimeter Films in Production
Built-Up Stockpiles Are Necessary (Up is an adverb here)
His Per Diem Was Increased (Per Diem is used as a noun here); Lower Taxes per Person (per is a preposition here)
3.50.

If a normally lowercased short word is used in juxtaposition with a capitalized word of like significance, it should also be capitalized.

Buildings In and Near the Minneapolis Mall
3.51.

In a heading set in caps and lowercase or in caps and small caps, a normally lowercased last word, if it is the only lowercased word in the heading, should also be capitalized.

All Returns Are In
3.52.

The first element of an infinitive is capitalized.

Controls To Be Applied

but Aid Sent to Disaster Area

3.53.

In matter set in caps and small caps, such abbreviations as etc., et al., and p.m. are set in small caps; in matter set in caps and lowercase, these abbreviations are set in lowercase.

Planes, Guns, Ships, etc.
Planes, Guns, Ships, etc.
James Bros. et al. (no comma)
James Bros. et al.
In re the 8 p.m. Meeting
In re the 8 p.m. Meeting
3.54.

Paragraph series letters in parentheses appearing in heads set in caps, caps and small caps, small caps, or in caps and lowercase are to be set as in copy.

section 1.580(f)(1)
Addresses, salutations, and signatures
3.55.

The first word and all principal words in addresses, salutations, and signatures are capitalized. See Chapter 16 "Datelines, Addresses, and Signatures."

Interjections
3.56.

The interjection "O" is always capitalized. Interjections within a sentence are not capitalized.

Sail on, O Ship of State!
For lo! the days are hastening on.
But, oh, how fortunate!
Historic or documentary accuracy
3.57.

Where historic, documentary, technical, or scientific accuracy is required, capitalization and other features of style of the original text should be followed.