Why adding ASW weapons can turn an OPV into a frigate

How easily could torpedo tubes or an ASW mortar be fitted to a modern offshore patrol vessel?

The launcher may be manageable, but a credible ASW system requires sensors, power, people, and support that can rapidly transform the OPV into a frigate.

Adding torpedo tubes or an ASW mortar requires targeting data, command links, hull stability, and appropriate sensors as well as deck space. Denmark's StanFlex simplifies changes where the ship already has prepared modular fittings. A Sting Ray lightweight torpedo still weighs about a quarter of a tonne, while an offensive heavyweight fit such as Spearfish would involve weapons nearly two tonnes in weight and seven metres long. Finding and tracking the submarine remains the harder problem. A towed array or helicopter sonar could give an OPV a useful role within a wider force, but either requires substantial integration. New systems need power, computing and operators, followed by more accommodation and support staff. Continuing that process can produce a roughly 6,000-tonne frigate.