Roy Palmer ("What a Lovely War")states: "...Lewis Winstock's Chelsea Pensioners told him that the song [Bless 'em All] was current in the army by the last decade of the nineteenth century. However, C.H. Ward-Jackson suggested that it, 'or rather a version not intended for publiction', was written in 1916 by one Fred Godfrey, while he was a member of the Royal Naval Air Service. It seems more likely that Godfrey was merely writing down a sond which was in circulation among servicemen in his day.
In turn, Jimmy Hughes and Frank Lake were responsible for an arrangement which became popular with civilians.... Soldiers sang both sanitised and scurrilous words, depending on the the company in which they found themselves. There were versions for sailors, paratroops....bomber pilots...and coastal command flyers. Canadian soldiers sang it. So did Americans, and continued to do so through the Korean War and into the late 1950s at least....."

Billy the Bus, The one of the best descriptions of the position of the RSM I'd heard of came in a spoof order which simply read

"Henceforth the Colonel will stand at God's Right hand (RSM to parade on Colonel's left)"

Good luck.

Walrus