Do not use that gun.

It's a anti submarine warfare.
IT cost way too much for low lvl people, and you may quit because you can't keep going on.

Anti submarine* warfare, yes. They're hedgehogs, a type of depth charge that's launched instead of dropped.

The 7x7.2" mark 11 is a premium weapon, which means you need to spend olives on ammunition. The 5x7.2" mark 10 is not premium, but as Richard pointed out it's very expensive (500 credits per salvo per launcher).

They're also not as effective as well-aimed cannon fire, though a lot of players use them as a crutch. Don't rely on them, because there's a good chance their effectiveness against surface ships will be reduced. You would also risk neglecting your cannon skills, which are very important later on in the game.

better stop using it NOW before your going to be bankrupt in using normal hh, or you'll suffer like the player that posted in the technical support his credit problem