Cannons and cutlasses might have kept the pirates of yesteryear at bay.
But not so for modern-day pirates, who troll the seas with GPS systems, satellite phones and rocket-propelled grenades.
As piracy off the coast of Somalia escalates to unprecedented levels, ships are turning to a growing arsenal of high-tech, nonlethal weapons to protect themselves.
Even the sly Jack Sparrow of the "Pirates of the Caribbean" franchise would have a tough time contending with the earsplitting sirens, pain rays and radiation systems ships are starting to deploy.
The number of attacks in the seas off East Africa has doubled in the past year, according to the International Maritime Organization, the London-based United Nations organization charged with improving maritime safety. As of the end of November, the group had received reports of 120 attacks, compared with 60 in 2007.
Maritime experts say that not only have the number of attacks increased, but the modus operandi of the criminals has advanced as well.
But despite widespread recognition that ships are increasingly vulnerable to pirates who attack ships with grenades and automatic weapons, vessels continue to hit the high seas without equally powerful defenses.
"Oil tankers, chemical tankers -- owners and skippers, insurers and legal guys -- no one wants lethal weaponry onboard," said David Johnson, managing director of the London-based MAD International, a distributor of magnetic acoustic devices, or MADs.
International guidelines strongly discourage ships from carrying or using firearms at sea. Deadly weapons could both intensify an already dangerous situation and become additional targets for attackers, a spokesman for the International Maritime Organization said.
Additionally, in some jurisdictions, he said, killing a national may have unforeseen consequences, even for a person who believes he or she has acted in self-defense. Other experts warn that firearms aboard a ship carrying petroleum could damage oil tanks and result in an environmental catastrophe, such as oil spills and leaks.
Litigation and insurance issues also factor into the decision to leave ships unarmed.
"There's no option but to use the best [non-lethal] equipment out there," Johnson told ABCNews.com.
Many ships are now starting to use MADs and long-range audio devices (LRADs), which can deliver loud and clear sounds to great distances across the water.
Vahan Simidian II, CEO of the Costa Mesa, Calif.-based HPV Technologies LLC and the developer of the technology, said the sound is emitted in focused parallel beams, much like a laser beam of light. As long as you are within a line of site, you can receive a clear, loud sound up to a mile and a tenth away.
His device, based on planar magnetic technology, can be used to hail and communicate with oncoming attackers. It can also be used to emit an unbearably loud noise that can help disorient and delay hijackers.
"I can make your ears ring so bad you can hardly think," he said, adding that though the sound will not knock someone off his feet, it will definitely push him back.
"It could severely hurt your hearing if it was prolonged, depending on how close you get and how long [you're exposed to it]," Simidian said.