military time

Military time is a four digit number from 0000 (midnight) to 2359 (one minute to midnight). Hour times (eg: 6am) are pronounced 'oh-six-hundred'. Other times (eg: 11:30pm) are pronounced 'twenty-three-thirty'.
It's useful in programming because you don't have to worry about parsing the colon (:). Just take the integer and modulus after dividing by 100 and you have the hours and minutes.

Military time zones span the area 7.5 degrees on either side of the meridians, starting with the Prime meridian in Greenwich (0 degrees). This time zone (UTC) is called Zulu time, since zero starts with the letter Z.

From Zulu moving east, the time zones are centered on the following meridians. The time zones do not always run straight on the meridians with a 15 degree span, since local time zones are also considered.

Degrees  Zone     Time  Difference (UTC)

  0      Zulu     Noon    0
 15 E    Alpha    1300    1
 30 E    Bravo    1400    2
 45 E    Charlie  1500    3
 60 E    Delta    1600    4
 75 E    Echo     1700    5
 90 E    Foxtrot  1800    6
105 E    Golf     1900    7
120 E    Hotel    2000    8
135 E    India1   2100    9
150 E    Kilo     2200   10
165 E    Lima     2300   11
180 EW   Mike2    2400   12  
180 EW   Yankee2  2400   12
165 W    Xray3    0100  -11
150 W    Whisky   0200  -10
135 W    Victor   0300   -9
120 W    Uniform  0400   -8
105 W    Tango    0500   -7
 90 W    Sierra   0600   -6
 85 W    Romeo    0700   -5
 60 W    Quebec   0800   -4
 45 W    Papa     0900   -3
 30 W    Oscar    1000   -2
 15 W    November 1100   -1
  0 EW   Zulu     1200    0

¹: I does appear as a zone. J (Juliet) is skipped, but refers to local time of the observer.
²: M and Y both refer to the International Date Line. Usually, M is west 7.5 degrees; Y is east 7.5 degrees.
³Note the change in letters and time difference.