British motor torpedo boats needed opportunities

Did Britain use PT boats against heavy ships?

Yes, dog boats and similar craft did when they could, but the smaller enemy battlefleet limited their chances compared with Germany's opportunities.

Combat records reflect opportunity as well as weapon effectiveness. Britain possessed many more capital ships than its opponents, so German light forces naturally encountered more heavy targets. British dog boats and related coastal craft did attack larger ships when circumstances allowed, including in waters off Norway. Their thinner record against capital ships therefore reflects the scarcity of suitable enemy targets as much as any lack of willingness to use the boats aggressively.