Question:  The Ordnance QF Hotchkiss 6 pounder gun were introduced to defend against watercraft capable of independent operation underwater usually referred to as "boats" rather than what?
Sentence (from "QF 2-pounder naval gun"): The 2-pounder gun, officially designated the QF 2-pounder (QF denoting "quick firing") and universally known as the pom-pom, was a 40 mm British autocannon, used as an anti-aircraft gun by the Royal Navy.
Relevant evidence: No