0 , ▁Royal ▁Navy ▁rum ▁was ▁ 9 5 . 5 ▁proof , ▁or ▁ 5 4 . 6 % ▁alco hol ▁by ▁volume ; ▁the ▁usual ▁r ation ▁was ▁an ▁e ighth ▁of ▁a ▁pint , ▁dil uted ▁ 2 : 1 ▁with ▁water ▁( 3 : 1 ▁until ▁World ▁War ▁II ). ▁Ext ra ▁rum ▁r ations ▁were ▁provided ▁for ▁special ▁celebr ations , ▁like ▁T raf al gar ▁Day , ▁and ▁sail ors ▁might ▁share ▁their ▁r ation ▁with ▁the ▁cook ▁or ▁with ▁a ▁mess mate ▁celebr ating ▁a ▁birth day . ▁Until ▁the ▁early ▁ 2 0 th ▁century , ▁" six ▁water ▁gro g " ▁( rum ▁dil uted ▁with ▁water ▁at ▁a ▁ 6 : 1 ▁ratio ) ▁was ▁sometimes ▁issued ▁as ▁a ▁pun ishment ▁to ▁sail ors ▁found ▁guilty ▁of ▁d run ken ness ▁or ▁neglect . ▁ ▁Over ▁time ▁the ▁distribution ▁of ▁the ▁rum ▁r ation ▁acquired ▁a ▁fixed ▁form . ▁At ▁ 1 1 AM , ▁the ▁boats w ain ' s ▁mate ▁pip ed ▁" Up ▁spirits ", ▁the ▁signal ▁for ▁the ▁pet ty ▁officer ▁of ▁the ▁day ▁to ▁clim b ▁to ▁the ▁quarter deck ▁and ▁collect ▁the ▁keys ▁to ▁the ▁spirit ▁room ▁from ▁an ▁officer , ▁the ▁ship ' s ▁co oper , ▁and ▁a ▁det achment ▁of ▁Royal ▁Mar ines . ▁In ▁process ion , ▁they ▁un locked ▁the ▁door ▁of ▁the ▁spirit ▁room , ▁and ▁witness ed ▁the ▁p ump ing ▁into ▁a ▁k eg ▁of ▁one - e ighth