Military Time was the manner in which time was expressed in correspondence and orders.

AM & PM

At the start of the 20th Century, Military Time in the Canadian military was based on the 12 hour clock, dividing the day into AM (ante meridiem - midnight to noon) and PM (post meridiem - noon to midnight).

24 Hour Clock

On 1 October 1918, the British Army, as well as the Canadian Corps in France, adopted the 24 hour clock. This method of telling time was used by the Canadian Army for the rest of the century.

The following is an excerpt from a Second World War military pamphlet:

3. Time (a) Time will be described by reference to the 24-hour clock. Groups of four figures followed by "hrs" will be used. The first two figures represent the hour, and the last two the minutes past the hour.

Examples (3 September)

• "0001 hrs" : one minute past midnight, night 2/3 Sep.

• "0900 hrs" : nine o'clock in the morning.

• "1200 hrs" : noon.

• "1635 hrs" : twenty-five minutes to five in the afternoon.

• "2400 hrs" : midnight 3/4 Sep.

 

AM	PM
1 o'clock 0100 hrs	1 o'clock 1300 hrs
2 o'clock 0300 hrs	2 o'clock 1400 hrs
3 o'clock 0300 hrs	3 o'clock 1500 hrs
4 o'clock 0400 hrs	4 o'clock 1600 hrs
5 o'clock 0500 hrs	5 o'clock 1700 hrs
6 o'clock 0600 hrs	6 o'clock 1800 hrs
7 o'clock 0700 hrs	7 o'clock 1900 hrs
8 o'clock 0800 hrs	8 o'clock 2000 hrs
9 o'clock 0900 hrs	9 o'clock 2100 hrs
10 o'clock 1000 hrs	10 o'clock 2200 hrs
11 o'clock 1100 hrs	11 o'clock 2300 hrs
12 o'clock 0100 hrs	12 o'clock 2400 hrs

Zulu Time

Zulu Time refers to Greenwich Mean Time, or the time in Greenwich, England. The use of Zulu time was to provide a consistent time standard when dealing across multiple time zones, local time variations (ie Newfoundland time, daylight savings time, double summer time, etc.)

History of Zulu Time

From Wikipedia:

Coordinated Universal Time or UTC, also sometimes referred to as "Zulu time" or Z, is an atomic realization of Universal Time (UT) or Greenwich Mean Time, the astronomical basis for civil time. Time zones around the world are expressed as positive and negative offsets from UT.

"UTC" is not a true acronym; it is a variant of Universal Time, UT, and has a modifier C (for "coordinated") appended to it just like other variants of UT. It may be regarded as a compromise between the English acronym "CUT" and the French acronym "TUC" (temps universel coordonné). It is sometimes erroneously expanded into "Universal Time Code". Originally, the local time at the Royal Greenwich Observatory in Greenwich, England was chosen as standard at the 1884 International Meridian Conference, leading to the widespread use of Greenwich Mean Time in order to set local clocks. This location was chosen because by 1884 two-thirds of all charts and maps already used it as their prime meridian.

The UT time zone is sometimes denoted by the letter Z since the equivalent nautical time zone (GMT) has been denoted by Z since about 1950, and by a "zone description" of zero hours since 1920. Since the NATO phonetic alphabet and radio-amateur word for Z is "Zulu", UT is sometimes known as Zulu time.

Date Time Groups

The use of date/time groups in messages was standardized, with the following format:

ddhhmmZ mon yy where dd=day of the month, hh=hour, mm=minutes, Z indicated Zulu time, mon=month and yy=year. For example, 220500Z JUN 93 would be the 22nd of June 1993, at 0500hrs Zulu time.

Approved abbreviations for months were Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec. Three-letter codes were adopted as standard to prevent confusion when writing date groups such as 03/04/76 which could man either April 3, 1976 or March 4, 1976 depending on personal interpretation.