John Gray, didn't the Allies in WWI build one of those LRADs? I remember reading about it, somewhere. Can't be too technical.
The pirates would, of course, buy something that they could hit back with. The obsolete 'Blowpipe' or another anti-tank weapon, at a guess.
The pirates don't seem to be very savage, trying NOT to kill people, trying to make a living in a mad country which has no security for anyone. Hardly the 'Dead Men Tell No Tales' type. Starting an arms race with them wouldn't help to keep that attitude going.

Like everyone, I can't think of a good answer to the problem. Especially as (I suppose) Foreign Aid has dried up.