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 = (713000*9.81 / sin(2*45))^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 = 0.5*8432800*2644.72^2 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.