Looking for an assault flotilla unit

Hi. I'm researching the people from our village who served in WW2 to include in our local history group's second book. I'm looking at the story of George Edward Preston who didn't turn 18 until February 1943, so we're in the later years of the war. The only clue I have is a photo on the winners of the drill, boxing and athletics trophy, taken (I think) at Exmouth / Lympstone. The label says 559 Squad. I've been trying to find out something about 559 squad and which operations they were involved in. The only other piece of information was a reference to an Acting Temp Major Nevil Reginald Poole of 559th Assault Flotilla mentioned in despatches June 1944 in Operation Neptune.

So, I'm thinking that the 559th were involved in the D Day landings, but were they shuttling troops to the beach? Did they come home or join in the fighting in France and beyond?

Which part of the marines / commando organisation were they in? I find the whole structural organisation really confusing and it seemed to change during the course of the war.

I'd really appreciate it if you could find some information about 559 squad and what they were doing in 1943, 44 and 45. I can send the photo if it's of any interest.

Many thanks

Sue Lyall