You most certainly would! SLBMs took until the eighties to reach ICBM range (5500km+). Previous SLBM were rather IRBM or even MRBM for the early sixties. Also, SLBM were substantially less accurate, being launched from a moving platform which has to find out it's own position first). Another thing is throw-weight ICBM can carry more and heavier warheads until the miniaturisation of the seventies and eighties.The Nazis had plans for submarine-launched missiles even during the war OTL, so you can bet they would probably the first to get SBLMs in this scenario, so you wouldn't necessarily need land silos anyway.