Believed to be 3rd Battalion, D Coy . They raided the house, but appear not to have found the target(s) they were looking for. However they did apprehend T/Cadets Garniss and Morris (in civilian clothes) who were on their way to Beggars Bush for reinforcements for the action at 22 Lower Mount St
There appear to have been 3 or 4 men outside the front of 16 Northumberland RD, on Guard duty. They stopped the two Auxiliaries in the street, took them throgh the house to the back garden, and shot them there.
And a group meanwhile had entered the house and been unable to find any suitable targets. It looks like a "standard" size operation of around 12 men in total
WS 487 of Joe O'Connor says it was D Coy, 3rd Battalion. He gives a list of men in Coy, but I am unsure of accuracy..