The Philippine Navy has been arming small patrol boats with portable anti-tank missiles, such the Israel's Spike. This is a fire and forget missile, which has a range of about 8 kilometers. Its easy to operate, even when the launcher is bolted to the deck of a small speedboat. The seagoing Spike has proven useful in dealing with pirates, since the missile reportedly can blow out a hole in the hull of a fleeing, fast moving, pirate ship.
Other small navies seem to have done much the same thing for small patrol vessels and improvised fast attack craft, such as the popular Boghammer. Aside from their value in providing some serious firepower for small patrol craft, such light anti-tank weapons (under a hundred pounds for launcher, control system and one missile) have considerable potential value for terrorists. In some areas of the world the seas are fairly crowded with large numbers of small vessels, from fishing boats to trading vessels, through which large merchant ships and even warships have to make their way. With an 8 kilometer standoff, a weapon like the Spike could do considerable damage to a merchant vessel, or even a warship, if not physically, then at least symbolically. While the Israelis are careful who they sell the Spike to, similar Russian missiles, like the Kornet, have been known to find their way on to the black market.