31 April

As promoted on the UNIT website, 31 April 2005 was the day of UNIT's Third Annual Extreme Ordnance Testing Day at the Aldershot Proving Ground, in which all UNIT personnel were welcomed to test the new TM 9-2330, as well as to use classic artillery such as the RR-3390 and the RS-8020. (PROSE: UNIT News)

Behind the scenes
In the real world, the month of April has only 30 days.