Hello
I believe the original commission for the gun was taken from Lt Cdr John Robert Guy Moncreiffe (I think there is a spelling mistake on the bill of sale).
Not the history of the gun I'm afraid, but a little about its first owner.....assuming the trailing 'e' was missed.
Lt Cdr Moncreiffe was the commanding officer of the submarine HMS E17.
In the morning of Thursday 6th January 1916 E17 was on patrol north of the island of Texel. The Submarine struck an uncharted bank and was badly damaged. The Dutch Cruiser Noord Brabant closed to investigate the problem but Lieutenant Commander Moncrieffe dived the Submarine to escape - believing that the Cruiser was hostile.
The damage forced Moncrieffe to surface. The crew was taken off and interned in Holland for the duration. Initially the crew was interned at Den Helder but they were later moved to Groningen where other Royal Navy internees were held. E17 sank later in the morning of 6th January
Its conning tower was later recovered and is preserved as a momument at the Royal Navy Museum in Gosport UK.
Hope that adds a little more colour to the sale.
FN