Torpedo puffers are typically Auriglobus species, and so named because these puffers, when young especially, are hyperactive, bombing around the tank like little torpedoes. Auriglobus are primarily freshwater puffers and not especially fussy about water chemistry. They sometimes occur in brackish water, and adding a little salt (3-5 g/l) may be useful if your find your specimen prone to fungal or bacterial infections. Generally this isn't required though. They are, however, incredibly nasty fish, both towards one another and any other unfortunate fish kept with them. They get to about 10 cm, plus or minus a few cm depending on the species. Auriglobus modestus and Auriglobus nefastus are probably the two most commonly sold species.
Chonerhinos silus may sometimes be sold instead of these fish. Care is similar to Auriglobus and visually they're practically identical. Xenopterus naritus is another species that might get confused with Auriglobus. It is a brackish water species, but otherwise similar; accord to Klaus Ebert, Xenopterus naritus has a yellow rather than white belly, so shouldn't be too difficult to tell apart.
Cheers, Neale