April 13, 2009  -- At least one former SEAL was not surprised that each of the three Somali pirates was killed with just one shot, despite the fact that they were on a rolling sea and the Navy snipers had to make a successful "head shot," something he said is "extremely difficult."

Their job was made easier by the pirates' willingness to allow their boat to be towed, smoothing out the sea and settling them into an even keel.

SEAL sharpshooters are trained to hit targets "under a minute," meaning they are able to hit within an inch of a target from 100 yards, former Navy SEAL Harry Humphries told ABCNews.com.

For the snipers who killed the three Somali pirates, it had to be a "head shot," Humphries said, because one of the pirates was holding an AK-47 pointed at the back of American freighter captain Richard Phllips.

"There's only one way to be assured no involuntary trigger squeeze, and that is a head shot," Humphries said. "If you hit the central nervous system, the probability [of an involuntary trigger squeeze] is greatly reduced."

"The shot's extremely difficult to make depending on equipment that shooters have," he said. "If the sea was flat, the shot would be relatively simple."

During the five day standoff, the Navy worked to get close to the pirates, but as their patience wore thin, the seas became rougher. The waves turned the lifeboat into a moving target, and the rear of the U.S.S. Bainbridge where the snipers were deployed was also heaving with the waves.

The Bainbridge convinced one pirate to come aboard the Bainbridge to seek medical attention and the other pirates allowed their lifeboat to be towed out of rough seas to a calmer area.

During the towing, the boat was pulled to within 40 yards of the Bainbridge, and the act of towing made the snipers' jobs easier by putting their lifeboat in the middle of the large ship's wake which calmed the unruly waves and steadied the pirates as targets.

The combination of the one less pirate and the others on steadier water would have "put the sniper team in excellent condition," Humphries said.

SEALs' Constant Training

With a gun pointed at Phillips' back, and tensions rising, the commander on the scene feared for the captain's life and gave the green light for the snipers to fire.

Standard procedure is for the shooters to be accompanied by a spotter who will gauge the range precisely and any weather conditions that could affect the shot. At times there is also someone to coordinate multiple shooters and to initiate the firing since it is essential in a circumstance like this that they fire simultaneously. That role can also be filled by one of the snipers, Humphries said.

When two pirates exposed their heads and shoulders, and the third pirate was visible through a small window of the lifeboat, they fired. All three fell dead.

Humphries said SEALs' training requires they be ready for such an emergency at any time.

"It's the constant training" under realistic conditions, he said, including from a bobbing ship.

"They are trained to shoot in sea, air and land," Humphries said, echoing the SEALs acronym for Sea, Air and Land.

"Secondly, you know the weapon that you're shooting. The weapon is very important," he said. Their weapons were likely modified M-4 rifles, he said, since it wasn't a long distance shot.

There are also different strategies for what SEALs call the "cold shot," or the first shot.

"A cold shot requires different setting than follow-ups," he said.

Vice Adm. Bill Gortney called the simultaneous shots "phenomenal," and President Obama said how "very proud" he was of the job carried out by the military.

But while Humphries praised a job well done, he wasn't surprised by the deadly outcome.

"It's a standard, well executed hostage rescue tactical solution... They had no other choice," Humphries said. "[This was] the only way they get the job done."

"It's not a bunch of cowboys out there," he said. "It was a very controlled situation."