Date-time groups, DTGs, are a way of writing the date and time (no, really?) as well as the time zone, usually within the military. They are used in orders, logs, and in my case a multi-time-zone flight.
DTGs are formatted as DDhhmmZMMMYY. For example, right now it’s 16:25 on 7 August 2014 in the UK – as a DTG, 071625AAUG14. The letter immediately after the time is the time zone – A being UTC+1 (British Summer Time) and Z being UTC (for most purposes, equivalent to Greenwich Mean Time).
Time zone designators
UTC -12: Y, UTC-11: X, UTC-10: W, UTC-9: V, UTC-8: U, UTC-7: T, UTC-6: S, UTC-5: R, UTC-4: Q, UTC-3: P, UTC-2: O, UTC-1: N, UTC+-0: Z, UTC+1: A, UTC+2: B, UTC+3: C, UTC+4: D, UTC+5: E, UTC+6: F, UTC+7: G, UTC+8: H, UTC+9: I, UTC+10: K, UTC+11: L, UTC+12: M