This little snap shot came with a bundle of other photographs. It is very small, out of focus and taken from some distance away. Given that there are soldiers on parade and that that the man himself appears to be surrounded by staff officers, it might just be him. I will leave it to you to decide.
Would American soldiers in Britain not be reviewed/inspected before D. Day? Perhaps given a rousing speech before departure?
Americans wore those M1917 helmets when they first arrived in Northern Ireland. By 1944 they had been replaced with the M1. Churchill was photographed wearing that outfit.
The chap in the background with the coat over his arm is Churchill’s personal protection officer of many years standing - DI Thompson. Walter H. Thompson - Wikipedia Steve
Photo taken in Iceland . Winston Churchill inspecting American marines in Iceland during his return from the meeting with President Roosevelt at Newfoundland. August 1941 Stock Photo - Alamy More pics here. Outpost in the North Atlantic: Marines in the Defense of Iceland