The short answer is that you want the 'snooker table', and probably an elaborate one at that.
Billiards, which was very popular with the military in India, is the parent game of snooker by about 75 years, the latter being 'invented' by Sir Neville Francis Fitzgerald Chamberlain KCB KCVO KPM in Indai in 1875.
http://en.wikipedia.org/wiki/Neville_Francis_Fitzgerald_ChamberlainVery much a gentleman's sport at the time, due to the size and expense of the tables, an officers' mess, gentlemen's club or gentleman's residence would have a billiards room, probably with one table in it. The precursors of billiards had been played in coffee houses in England in the C18th but most of those had died out by the turn of the C19th, and snooker halls came later. The illustration sjwalker51 posted is interesting as the table is not of modern proportions, but since the English Billiards Association did form until 1885 I suppose there may have been no regulation size before then; alternatively, the artist may not have been familiar with the games tables of the gentry. However, if it is too square it would be a difficult to play in the middle.
Militarily, it would have the great advantage, if tipped on its side, of providing you with a 12' x 6' firing position protected by at least 1" of high-quality slate! I doubt the defenders missed this opportunity unless they were more afraid of the wrath of the President of the Mess Committee for ruining the 'lie' of the table....