Good man! I knew you would be out there somewhere to put the record straight!As it happened old bean,, dug out my scan of the history the other day to help the D-Day 75 planners...
The document is called THE STORY OF THE MULBERRIES, written in 1947 for the War Office by Rear Admiral Hickling (NOIC of Mulberry B) and Brigadier Mackillop (DQMG(Movements) 21 Army Group). It is a combination of engineering and operational history.
The photo from the OP looks to be an 80 feet span of floating roadway. WHALE referred, as others have said, to the overall equipment package to provide quickly erected piers to "provide continuous alongside discharge on flat beaches with a tidal range of up to 30 feet... able to withstand rough weather." It was one of the four main component packages, the others being the blockships, the BOMBARDON floating breakwater, and the PHOENIX caisson harbour-walls. The blockships and BOMBARDONS were naval responsibilities, PHOENIX and WHALE Army responsibilities.
WHALE comprised two principal parts:
a) the SPUD pontoon pier-head; and
b) the flexible floating roadway to link the pier-heads to each other, and, more importantly, connect them to the shore. Came in two classes - Class 40 for tanks, Class 25 for 10 ton lorries plus trailers.
The authors comment that the floating roadway was the most difficult design problem of the whole of the Mulberry project, and luckily one of the first to be tackled. The 80 foot spans as shown in the picture do not seem to have had a specific codename, but the pontoons on which they floated were BEETLES, so called as they were turtle-backed to dampen the wave motions. The BEETLES were also designed so that rubber bags could be inserted easily in them and inflated by a work boat as a temporary fix should they suffer strafing or bomb damage, to reduce the number of occasions a roadway would have to be shut down to allow a pontoon to be replaced. The BEETLES could also be fitted with legs to stop them coming into contact with seabed rocks at low tide. Beehive charges were used by divers to create anchor points for the BEETLES in rock.
There was also a variant span, which was telescopic and could vary between 71 and 80 feet - these were used every four or five standard spans, to cope with the extremes of spring tides - the problem otherwise would have been that you could not build the roadway at a neap tide, and not then suffer embarrassment when the springs rolled in. They were also used to connect the pierheads to each other - as the authors comment, it would otherwise have been "very tedious" to position the pierheads precisely 80 feet apart...
Worth mentioning, if not known, that each roadway span could twist safely up to 18 degrees end to end.
Overall WHALE production was 23 SPUD pontoon pierheads, plus 7 miles of floating roadway spans and BEETLES - 50,000 tons of steelwork made at 240 different factories in the UK, with assembly in the Clyde, at Southampton, and at Richborough. There was a back-up alternate design for the BEETLES in reinforced concrete, since steel-plate was a bottleneck, but these could only be used at the seaward end of the roadways as they did not handle grounding well. In any case, too many concrete BEETLES would in turn have risked a bottleneck on the construction of PHOENIX.