WASHINGTON -- At his kitchen table in Allentown, Pennsylvania, Pearl Harbor veteran Richard Schimmel shows me a small, laminated piece of paper. It's yellow and smudged from decades of aging, but the handwriting is legible, and it has a simple title: "Warning."

It's a note the 94-year-old wrote down in the early-morning hours of Dec. 7, 1941, cautioning of a large group of planes coming toward Oahu, Hawaii. Those planes turned out to be the Japanese heading toward Pearl Harbor, an attack that killed thousands of Americans and ushered the U.S. into World War II.

Schimmel wasn't on duty that morning, so he wasn't the one who received the actual warning. His friend and counterpart Joe McDonald did, and what happened with that note weighed heavily on him for the rest of his life.

"It really bothered him that he didn't do more. At the time, it would have been wrong, but I guess it would have been right, too," Schimmel said.

So what was it that bothered McDonald so much? Here's their story.

THE BEGINNING OF RADAR

Schimmel enlisted in the Army in late August 1940 and was shipped to Oahu a few months later to join the newly formed Signal Aircraft Warning Service.

"They asked me where I wanted to go, and I said, 'The cavalry,'" Schimmel joked. "The [recruiter] said, 'We don't have the cavalry anymore.' So he put me in Signal Aircraft Warning. I said, 'What's that?' And he said, 'I don't know.'"

Schimmel's job was to become a plotter and switchboard operator at the information center at Fort Shafter, just east of Pearl Harbor. But first, he had to help install the mobile radar stations that would bring in the data. Radar, after all, was new technology that England had just shared with the U.S.

"We didn't know what we were doing half the time because radar was so new, and nobody knew anything about it," Schimmel recalled. "But we finally got it working. … Not much earlier than September of 1941."

The 19-year-old private first class and his Army friends learned the ropes of radar over the next few months, but because leaders were worried they would wear the equipment out, they were only allowed to use it a few hours a day. No one was scheduled to be working at the Opana Radar Station in northeast Oahu the morning of Dec. 7, 1941, but by happenstance, two technicians were.

"It just happened that on Dec. 7, a guy by the name of George Elliot was learning to use the radar, and he was up at the [Opana] unit. Joe Lockard was over him and was teaching him how to use it," Schimmel remembered.

"George picked up the group of airplanes that were coming in. Joe at first dismissed it, but then he looked at it a second time and saw there was a lot coming, so he decided to call into the information center, which is where I normally worked at that time. But I had been relieved by Joe McDonald the night before."

A POSSIBLE MISSTEP

McDonald got the warning from Elliot and Lockard, and he passed it to the lieutenant in charge. The lieutenant assumed it was American planes, so he did nothing about it. McDonald remained concerned, however, and brought it to the lieutenant's attention again -- and was again told to forget about it. So he did.

"When McDonald left, he came up and gave me that message. He had written it down," Schimmel remembered, making his own copy of the note then and there. "He no sooner gave it to me and we were talking, then all of a sudden we heard noise and we looked out, and we could see smoke coming from toward where the ships were."

The bombing of Pearl Harbor had begun.

"George Elliott was the first person to know, then he told Joe Lockhart, who told Joe McDonald. Joe McDonald told the lieutenant, and I was there with them, so I was the fifth person to know," Schimmel said.

He and the others watched the attack for a few minutes, then quickly ran to the information center, where they would spend the rest of the day taking down details about the attacks.

LIFELONG REGRET

McDonald did what he was supposed to do that day, but following the rules was something he questioned for the rest of his life.

"He thought he should have gone over the lieutenant's head, to call somebody else. And I said, 'Joe, you can't do that, because you can't go over an officer's head -- not when you're an enlisted man.' And that bothered him," Schimmel said.

Schimmel believed that if there had been more time to set up radar stations on the other islands, there might have been less confusion about to whom the planes belonged.

"I think if you would have had the radar working near Honolulu, they would have been picking up the planes coming in from the states, which were coming west. But these planes were coming east, and if they realized that, they would have looked into it a little more," Schimmel said.

Whether or not that would have made a difference will always be debatable. As for Schimmel, his only regret was this: "Having only one life to give to my country."

After Pearl Harbor, Schimmel was sent to several other Pacific islands to help set up more information centers. He spent a total of 56 months overseas before the war ended in 1945. Schimmel left the Army soon after, got married and had two boys, Rick and Terry -- his proudest accomplishments.

75 YEARS LATER

At 94, Schimmel stays physically and mentally sharp by hitting up his local YMCA three days a week and planning group excursions to various destinations, including an upcoming trip to Hawaii for Pearl Harbor's 75th anniversary.

That busy lifestyle could be why his memories are still so vivid -- that's not the case for the recollections of many other World War II vets. So for the younger generation who may not know much World War II history, Schimmel had this to say:

"Just remember Pearl Harbor. What happened there can happen any time."