Considering the A-4/V-2 launch failure rate in optimal conditions, a single successful water launch
would be near miraculous.
As to the artillery rockets, a handful of subs with a handful of rockets would have done little lasting
damage to the New York port structure.
Also if the German's had managed to to carry off a semi-major attack against the US mainland, it's
likely that
all German cities would have been Dresdenized.