Why arming patrol vessels for ASW can backfire

Why not add anti-submarine torpedo tubes to patrol vessels?

Because the armament can create a false impression of full ASW capability and encourage substitution for properly equipped frigates.

Adding torpedo tubes to an offshore patrol vessel risks persuading politicians that it can replace an anti-submarine frigate. The patrol vessel would still lack the sonar, towed array, effective quieting, and helicopter needed for that role. Modern ASW also requires substantial computing power. Procuring the weapons alone could encourage missions that exceed the ship's equipment while weakening the case for buying properly equipped frigates.