Skua , 2 hours ago

For these purposes I am, of course, assuming that air resistance doesn't exist. Which would probably increase this answer by a lot.

Narva bay to Moscow = 713 km
Fully loaded Arleigh Burke destroyer displacement = 8,432,800 kg

v = launch velocity
d = horizontal distance = 713000 m
θ = angle we're launching the ship at = 45 degrees
g = acceleration (from gravity) = 9.81 ms^-1

Range of a projectile equation:

d = (v^2 sin(2θ)) / g

Rearrange to find v:

dg = v^2 sin(2θ)
dg / sin(2θ) = v^2
v = (dg / sin(2θ))^0.5

Plug our numbers in:

v = (7130009.81 / sin(245))^0.5
v = (6994530 / 1)^0.5
v = 2644.72 ms^-1

So we need to launch at 2,645 metres per second (9,522 kph, 5,917 mph). To get the energy, we use the kinetic energy equation:

e = 0.5 m v^2
e = 0.584328002644.72^2
e = 29,491,794,808,885.76 joules
e = 29.5 terajoules

For comparison, the nuclear bomb dropped on Hiroshima exploded with about 60 terajoules of energy. So once you account for air resistance you're probably looking at a nuke of energy.