The O and P design had trimmed the J hull in the hope of easier construction. The Q and R design went back to the full hull before the earlier batches had entered service. More hull volume allowed additional fuel, with a reported gain of roughly 1,000 nautical miles at 20 knots over other Royal Navy destroyers. That was useful for faster passages even though 15 knots remained the usual cruising speed. The usual fit included 4.7-inch guns, Oerlikons and a quad pom-pom, two quadruple torpedo banks and a nominal 45 depth charges.
Chapter · 42:49-45:00
Why the Q and R classes restored the full J hull
The next emergency destroyers restored hull volume for fuel and better endurance at 20 knots.