Why a calculating engine would not immediately become shipboard fire control

Would a working difference engine lead directly to naval targeting computers?

Not immediately, because reducing the large mechanical engine to a shipboard size would take time.

A working difference engine would not immediately give warships a practical targeting computer. The scale of the full mechanical machine is the obstacle identified. A smaller shipboard mechanism is considered a possible later development, after a lengthy period of miniaturization. The premise therefore separates access to faster calculations ashore from putting calculating machinery into a ship's fighting equipment.