Rincón, Puerto Rico - The first time former U.S. Army National Guard veteran John W. Thompson walked into Walter Reed he knew he had to do something.

"I've never been to a military hospital and one day I went to have lunch with my wife at Walter Reed and as soon as you walk in, you see some pretty heavy stuff and I really wasn't prepared for that and it hit me hard. I knew right at that moment that I had to get involved but I really didn't know what attributes I had to offer these guys," he said.

Thompson, who served in the Army National Guard from 1985 to 1992, said he "needed some direction and discipline."

"So I moved to Colorado and enlisted in the Army National Guard. The military gave me what I needed as a young man," said Thompson, who lost his father at the age of 13.

Thompson was never deployed - and seeing the young men and women at Walter Reed was a real "gut check" for him.

"I was lucky and they weren't so lucky," he said.

After his visit to the medical center, he went to the American Red Cross office at the hospital and asked to be a volunteer. He was placed in the aquatics department and started helping wounded soldiers.

It was there that Thompson realized he could help even more these soldiers with their rehabilitation.

Diving trip in Guantanamo Bay Naval Base in Cuba. SUDS

"Eventually I was you know what, here's a pool and all these injured men and women and I'm a certified diving instructor so why don't we use scuba diving to help with the rehab process, he said.

After that visit to Walter Reed, it has become Thompson's life passion to help wounded soldiers. He launched SUDS, Soldiers Undertaking Disabled Scuba in 2007, which is based at Walter Reed National Medical Center in Bethesda, Md.

The organization focuses on improving the lives of injured servicemen and women returning from Iraq and Afghanistan.

"We use Scuba diving and other adaptive sports to help facilitate the rehabilitation process for injured soldiers coming back from war," Thompson said.

SAMMC (San Antonio Military Medical Center) group diving last week in Panama City Beach. SUDS

"A lot of them are still going through treatment, a lot of people don't know this but some of them have had 75 or 80 surgeries. They have to go through multiple surgeries and to see the joy and excitement when we come up from the dive is amazing. They are away from all that stuff at home and here they can relax and have an enjoyable time," he added.

During the winter, Thompson brings a veteran each week to dive with him in the warm waters of Rincon, Puerto Rico, a surf town off the west coast of the island. Taino Divers, a scuba diving shop in Rincón takes Thompson and wounded soldiers off to the small island of Desecheo.

"It is a great place and I have been coming here for the past 12 years and it is a small town with about 15,000 people but most of the residents if they see an injured person or amputee they know that they are part of the SUDS program. They just roll out the red carpet and they treat them like family," Thompson said.

One of those veterans participating in the program is former U.S. Army Staff Sergeant Juan Andres Arredondo.

U.S. Army veteran Juan Arredondo. Juan Arredondo

Arredondo, 34, joined the U.S. Army in 1998 to provide for his family. He grew up in the Coachella Valley, Calif., where a lot of his friends enlisted.

"The friendships you form with the other service members that want to serve this country was the best part about being in service. There's nothing like it," said Arredondo, who was assigned to 1/506 D Company, 2nd Infantry Division based in South Korea.

Arredondo was deployed to Iraq in 2004. On February 28, 2005, Arredondo fears came true - his vehicle was hit by a roadside bomb.

"My platoon sergeant was with me in the truck and he looked over and he said, 'Arredondo, IED on the left side.' I knew what that meant in the kill zone so I just put my head down and my foot on the gas and that's when the device went off," he says. Arredondo's left arm was severed immediately. "When you're lying in the bed all you're thinking is about how you are going to take care of your family," he recalled.

He sustained multiple injuries to both his left and right calves, his right thigh, right arm as well as and his left hand was severed at the wrist.

"My recovery was tough. I was able to do things but it was my mind what was holding me back, telling me I can't do that," Arredondo said.

For Arredondo, the scuba diving training has been a rewarding experience.

"It is very important to have recreational therapy and sports like scuba diving because it gets you in the mindset that you can still operate and do what you want to do," he said.

The first time Arredondo went out scuba diving was also his very first time on a boat.

"I was very proud to do my first dive with John and on my first dive I got to see a whale shark," he said.

After that, he started scuba diving more frequently.

SUDS diving trip in Rincón, Puerto Rico. SUDS

"There's not a lot of weight down there. The weightlessness, the quietness, and the breathing of your regulator and oxygen tank is just very calming. It is an amazing feeling. It feels like I'm leaving all my troubles above the surface," he said.

SUDS runs about 12 scuba diving trips a year and they go to places like Hawaii, Curacao, Puerto Rico, Guantanamo Bay Cuba and the Gulf of Mexico.

"These guys end up being my closest friends," said Thompson. "It is very inspiring to see Juan with his injuries and others and see them overcome their injuries and not letting that define them. Juan has a lot of heart and spirit."

Second Tour is an ABC News digital series profiling the lives of military veterans who are doing unique things in the civilian world. For more stories, click here.

Juan Arredondo and John Thompson in Rincón, Puerto Rico after a dive in Desecheo Island. Angel Canales /ABC News

ABC News video editor Arthur Niemynski contributed to this report.