Then there was the other Great Idea - cats....
When the Navy's wooden wonders called in for a spot of shore time, the cleverest of their rats obviously though "Thank f*** for that, follow me chaps and we'll escape this life of rotten meat and squalor", then led his chums to freedom.
However, having no natural predators, the little $ods bred like crazy.
"Hmm", opined someone in the Admirality, "what can we do? I know - let's send some cats - they'll sort the buggers out!"
So Qty. Lots of pussy cats were duly rounded up and transported to Ascension. They probably didn't get much of a vote in this - and were undoubtedly rather peeved to be booted out to fend for themselves upon arrival.
A few spotted the odd rat, but chasing them across the volcanic wastes was rather painful on the paws. But then one of them spotted a bird. Now birds knew what rats were, because they stole their eggs. But they'd never met these furry things with four legs and a tail before, so went over to say hello....
Mistake. BIG mistake!
From that moment, the cats never looked back. Rats were far TFD, but birds were a piece of pi$$....
Hence the current feral moggy population at ASI.