Military time converter (24-hour time)

Keep AM hours as they are with a leading zero, write 12 AM as 00, keep 12 PM as 12, and add 12 to any other PM hour. Then write the hour and minutes as four digits without a colon: 7:45 PM is 1945 and 6:05 AM is 0605. Army Regulation 25-50 gives 1:37 p.m. as 1337 and says the word "hours" is not written after military time.

In hundreds, pair by pair. The US Navy's Basic Military Requirements manual gives 0100 as "zero one hundred", 2000 as "twenty hundred" and 2315 as "twenty three fifteen"; "hours" is usually added in speech, as in ACP 125's "sixteen thirty hours". Official sources say "zero", not "oh". On a radio net, date-time groups and times in poor conditions are read digit by digit: one six three zero, with nine said "niner".

Both appear. The Navy's Basic Military Requirements manual uses 0000 for the start of a day and 2400 for its end. The Navy correspondence manual (SECNAV M-5216.5) runs times from 0000 to 2359, while Army Regulation 25-50 runs from 0001 to 2400. ACP 121, the Allied communications standard, advises writing 2359 or 0001 in messages to avoid the ambiguity.

Zulu is the military name for UTC, the zone letter Z. Letters A to M (J skipped) are UTC+1 to UTC+12, N to Y are UTC−1 to UTC−12, and J (Juliett) means the observer's local time (Army ATP 6-02.70, Table E-1). Washington, DC in winter is zone R, UTC−5, so 1945R is 0045Z the next day. The letters are whole-hour offsets; ATP 6-02.70 marks a half-hour zone with an asterisk, as in 0430D* for Afghanistan (UTC+4:30).

It is how military messages stamp a date and time: two digits for the day, four for the time, the zone letter, then the month's first three letters and the year's last two digits. ACP 121(G) gives 271630Z JUN 03 as 16:30 UTC on 27 June 2003. Switch on "Write a date-time group" under More options to build one, in your zone and in Zulu.

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 11 worked examples whose answers come from independent sources; for example, “7:45 PM” is checked against Add 12 to a PM hour; spoken in hundreds per Navy BMR ch. 3; digit words and “niner” from ACP 125(G) Table 3-2.

US Army ATP 6-02.70, Techniques for Spectrum Management Operations (2015), Appendix E: time zones, Table E-1 (copy at bits.de); Combined Communications-Electronics Board, ACP 121(G) Communication instructions — general, para 317 and 325, Annex A to chapter 3 (copy at navy-radio.com); Combined Communications-Electronics Board, ACP 125(G) Radiotelephone procedures, Tables 3-2 and 3-3 (copy at Civil Air Patrol); US Navy NAVEDTRA 14325, Basic Military Requirements, chapter 3: military time (copy at navytribe.com); US Army Regulation 25-50, Preparing and Managing Correspondence (2020), para 1-26; US Coast Guard CGTTP 6-01.1B Radiotelephone Handbook (2018).