This is the site that 9 Para, including Private D.R. Hurley assaulted before dawn on D-Day, whilst other battalions of the 6th Airborne Division took Pegasus Bridge and other targets.
These bunkers were built to be camouflaged from the air.
Indeed on seeing this picture of a bunker at Merville, our youngest immediately said 'it looks like Pembrey Country Park.'
At the Country Park - the site of RAF Pembrey until 1957 and a Royal Ordnance Factory during WW2 and the Korea War - there are many bunkers almost identical in layout to the Merville bunker pictured here.
The Kidwelly History site says of the Royal Ordnance Factory at Pembrey:
It was Britain's largest producer of TNT with 700 tons and produced 1,000 tons of Ammonium Nitrate and 40 tons of Tetryl at it's peak in 1942 and employed 2,000 people.
One can almost imagine the concrete entrance to the bunkers painted in camouflage paint, draped with camouflage netting and similar to disguise them from the air and reconnaissance efforts by the RAF and the Luftwaffe accordingly.
There is less earth on top of the French bunker, but given the severe aerial bombardment of the Merville Battery, there's little wonder that the actual bunker had less natural coverage.
The picture below shows the Merville Battery with the gun bunkers circled. It shows the extent of Allied bombing on the site which, if nothing else, must have unnerved and demoralised the defenders.
According the official Merville Museum site (see link in right hand panel), the Merville Battery received:
The most intensive bombing (in excess of 1,000 bombs dropped by 109 Lancasters) of the night of 5th/6th June.
As usual the programme is more than a little cheesy and open to all manner of interpretation, but it also gives a good overview and intro to the Country Park and its former occupants and usage. You can see the bunker with the double decker bus in it on part one of the show.
Merville on French Wikipedia (more info than its English version)
Kidwelly History on RAF Pembrey