U.S. ships in the area engaged in monitoring the yacht included the aircraft carrier USS Enterprise, the guided-missile cruiser USS Leyte Gulf, the guided-missile destroyers USS Sterett and USS Bulkeley. The ships are deployed to the region to conduct maritime security operations and to provide support to operations Enduring Freedom and New Dawn.
The 58-foot S/V Quest is owned by Jean and Scott Adam, who had been sailing the boat around the world for the past seven years. As they approached the notoriously hostile waters off the Horn of Africa, the Adams cut back using their radios and satellite systems so their location couldn't be tracked by pirates, but they were still found.
The Adams were members of the Del Rey Yacht Club in Marina Del Rey, Calif. The couple had been detailing their travels on a website, where an entry from last December listed their expected stops in 2011 as "Galle, Sri Lanka; Cochin, India; Salalah, Oman; Djibouti, Djibouti; The Suez Canal; and Crete. That gets us to April."
That path would have taken them directly into the pirate-infested waters off the coast of Somalia. Pirates there have seized oceangoing vessels for large ransoms; just last week two supertankers carrying oil were seized in waters far off the Somali coast.
MacKay and Riggle were on an extended leave from their lives in Washington and a friend said Monday he was surprised to learn they were on the Adam's boat since they had their own boat too. The couples had apparently linked up in India, according to her friend John Eggers, who appeared Monday on "Good Morning America," before the shooting.
"What I heard is that they hooked up I guess in India, and they joined the Adams, which is pretty common in the sailing industry I guess. People hook up on boats and take off," said MacKay's friend, John Eggers.
"Phyllis has been sailing for quite a few years. She's been on leave now for about three years. She called one night and said she was going to go on sabbatical, said she'd be back in a year, year and a half, and now it's going on three years," said Eggers. "It was a surprise but she is a very independent, very strong woman. She was at the peak of her career in our industry so it was surprising to me and she was just very respected but she wanted to go on this leave with Bob and away she went."
The last time pirates targeted an American vessel - the Maersk Alabama in 2009 - the heist ended with all but one of the pirates killed by US navy sharp-shooters.
The challenge for international warships now is keeping the pirates from making it to the Somali shore where they and their hostages can easily disappear.
Pirates held British couple Paul and Rachel Chandler for 388 days until they were paid a ransom believed to be above $1 million.
It is believed that Somali pirates currently have 29 ships in their possession and are holding 660 crewmembers hostage.
Pirate seizures have continued in the waters off East Africa despite the constant patrols of by the world's navies, including ships from the United States.
Last Thursday, Abdiwali Abdiqadir Muse was sentenced in New York to 33 years in prison for kidnapping and brutalizing Capt. Richard Phillips, who was held hostage for five days in 2009 when pirates armed with AK-47s scrambled up the stern of Maersk Alabama.
The U.S. Fifth Fleet, based in Bahrain, coordinates an international task force that patrols the waters of East Africa. The European Community also maintains a separate anti-piracy mission in the same waters.
ABC News' Dana Hughes, Steven Portnoy, Kevin Dolak, Luis Martinez and Jeremy Hubbard and Z. Byron Wolf contributed to this report.