[eliex]

Yeah, it has been a tactic I now always use when it comes to replaying BP; Forced Entry in particular. 
In INF, Shivan Ultra Bombs were odd in the sense that the AI fires the bomb at the maximum range - 3000m IIRC so they never really kill their intended target.

[Dragon]

Quite fortunately ,a few of those was enough to blow up any target smaller than Sathanas ,and even for Sathanas you wouldn't need much of them.
The Icalus you was defending in "El Diablo" never stood a chance of survivng more then five hits ,not to mention that there was other ships firing on it ,so it really could take around three.

[eliex]

This is another example of Inferno overpowering a ship's weapons; it's one of the main criticisms from the FSWiki.
However, have you ever tried out the secondary weapon "Armageddon"? You need to cheat to obtain it but upon impact that bomb really creates a bang.

[ssmit132]

It also flings smaller targets at a high rate of speed towards you. So look out if you use them on cruisers and the like.