"the Walrus was a seaplane carried on deck"

The significance of hitting the seaplane was that it had fuel tanks - petrol. The reason that the damn things were hated so much and normally launched before any expected artillery exchange was that if hit, it spilt flaming fuel over a significant part of the ship, immobilizing some of the weaponry, possibly causing ignition of explosive armaments, and inhibited the crew from using the normal proceedures to use the ships weapons, as well as distracting them by having to fight a Class C fire - with only seawater to use - while under enemy fire...