Rapid development in the late 1930s and during World War II left fleets operating several generations of fire-control equipment. Refitting every ship with the latest system would have removed ships needed for convoy protection and battle operations. Navies therefore had to keep mixed installations in service. A newer system could also perform worse if its design rested on a faulty premise or introduced problems that had not been anticipated.
Notable Point · 2:55:29-2:56:33
Why wartime fleets kept mixed fire-control systems
Convoy and battle commitments prevented universal upgrades, while unanticipated design problems sometimes gave older fire-control systems an advantage.