Ship Gun Fire-Control Systems

Ships have a tendency to accelerate, turn, pitch, and roll, often unpredictably while at sea. Assuming your ship has a good reason to fire upon another ship (say, it's staffed by the baddies), this can make successful targeting difficult. The problem of how to make friendly shells hit enemy ships more often was one of the key drivers behind the revolution in computational speed in the 20th century, and you can read more about it, and its solutions, here:
Ship gun fire-control systems

Given the crash pace of computer development during the 1930s and '40s driven by the need to converge on better targeting solutions faster at war, it's no surprise Heinlein chose to make Mike the self-aware Lunar governing computer an overclocked, massively upgraded ballistic calculation computer. It's easy to forget how different the manufactured world is now than it was a century ago, when automation was rare and often as much a nuisance as a help. As late as World War I, when sailors had to do almost all the work themselves to target enemy ships, 3% of shots reaching their targets was considered excellent accuracy. Now that the machines we make work so hard to help us, we can manage a fair bit better.