I haven't the slightest idea about what it is, but I would guess it is from the older end of the 1955-1985 scale. The designers were clearly digging on 20,000 Leagues Under the Sea w/ Kirk Douglas. (released in 1954)
The 18’ Swimmer Delivery Vehicle (SDV) MK 7 MOD 6, commercial designation Convair Model 14, was the standard underwater transport used by UDTs and SEALs during the late 1960s and early 1970s. The first American-made SDV, it replaced the Italian-made MK 6 MOD 0 Sea Horse. The first SDVs were used by SEAL Team One back in 1969, when the entire SDV platoon consisted of no more than two officers and less than a dozen enlisted men. It could be deployed from the LPSS-574 Grayback, a modified Regulus II class submarine used for UDT and SEAL support starting in 1970. The submarine could carry four SDVs in its hangars.
The MK7 MOD 6 was a so-called “wet” or free-flooding submarine: the crew and passengers were immersed in water and must wear scuba gear and diving suits. Eight onboard 90-cubic feet bottles allowed semi-closed-circuit diving for up to 8 hours. The crew consisted of pilot and navigator seated in tandem. Two swimmers and 55 lbs. of explosives or other supplies could be carried. The MK 7 MOD 6 was made of non-magnetic plastic materials and could dive up to 200’. It had a 1.4-kW electric engine powered by six silver-zinc batteries.
The first photo is not of a Mark VII, what is the mystery SDV in the first post picture?