Good points dear apophenia,
The first Vertol 107 (Voyager) flew in 1958.
The first S-61 Sea King flew in 1959.
The first S-61R flew in 1963.
I suspect that even when folded (USMC pattern), Vertol 107/CH-46 was too big for RCN Destroyer Escorts (DDE). A folded Vertol 107 is 45 feet long by 15 feet wide.
Sorry that I do not know the folded dimensions of Sea Kings, but know that the 64 rotor diameter exceeds the beam of DDH 280 class destroyers. Even when folded, a pair of Sea Kings require a hangar the full width of the ship. Those hangars are also quite tall and catch a lot of wind. The large side surface and high centre of gravity contribute to rolls as much as 45 degrees! I have experienced 40 degree rolls aboard HMCS Iroquois that quickly exhausted sailors.
I am not sure about the stability of S-61R on the water.
On the subject of stability on the water. It may not be clear from photographs, but Sea King aluminum sponsons contain huge wheel wells, which halve the amount of floatation. Ergo, most Sea Kings were fitted with emergency floatation bladders on the outboard side of the aluminum sponsons. These inflated to roughly the same size as the aluminum sponsons, doubling roll stability.
Civilian S-61Ls had double-sized aluminum sponsons.
Many British naval helicopters had emergency flotation bolted to the outboard ends of main wheel axles.
Also note that Canadian Labrador and Swedish CH-46 had huge fuel tanks bolted to their stub-wing sponsons.
I suspect that RCAF SAR S-61R would receive similar, double-sized sponsons/fuel tanks.
A Canadian Sea King navigator told me an amusing anecdote, in 1984. He and some other Canadian aircrew had recently visited the Sikorsky factory to review the new S-60 Sea Hawk. They admired its simplified maintenance and improved performance but grumbled about how its tiny cabin was unsuitable for the "admiral's barge" ... er .... cross-decking the padre on Sunday mornings .... er .... long range SAR role ... er ... cross-decking cargo role. Yes, that is it: cross-decking cargo. When a Canadian suggested building a SH-60FH (Fat Hawk), Sikorsky engineers politely chuckled!
A few years later, Sikorsky announced that they were developing the S-92 which is essentially an S-61R fuselage hung under SH-60 rotors. S-92 incorporates a cargo ramp under the aft fuselage and was adopted as the Sea King Replacement.
Yes, I mentioned a long-range SAR role for embarked Canadian Sea KIngs. On a few occasions, Canadian ships were the closest to civilian ships in distress and rescued passengers with their personnel hoists. All RCN Sea Kings had personnel hoists permanently fitted above cargo doors.
As for upgrades - like Westland's six-bladed tail rotors - .... After the supply of original - American-made - tail rotor blades dried up, Canadian Sea Kings got five Westland tail rotor blades bolted to the their stock tail rotor hubs. I watched them doing hover trials at CFB Shearwater. New Westland-built blades looked the same to maintainers.
OTL all RCN Sea Kings were assembled at United Technology's factory near Montreal. They just bolted together parts made by Sikorsky. They hoped to assemble more S-61s for civilians, but those contracts never came.
ATL I can forecast Sikorsky sub-contracting for simple, sheet metal components, but keeping drive train production in house. That would see Canadian Sea King sheet metal production farmed out to Canadair, Fleet, Bristol, etc. ... whichever federal riding needed to buy a few more votes. That would allow politicians photo opportunities beside, big, shiny, impressive pieces of aluminum airframes. Though it makes sense to only use 1.5 sets of jigs to build all the fuselages. Stock forward and mid fuselages would be build on one set of jigs with the two different aft fuselages built on separate jigs and only riveted on late in production.
Sea King and Commando side doors are too high above the deck for heavily-laden infantry to climb aboard without extra, external ladders.
