Over two decades, Air Force Col. Arthur Ahl has left his mark on Northwestern High School's Junior Reserve Officers Training Corps program.
The former pilot has boosted enrollment, added incentives - like flight simulators and Nintendo Wii - for students and helped expand ROTC across York County.
During the summer, he teaches a leadership program with specialized science and math lessons created by the National Science Center, which Ahl has fine-tuned.
So it's no surprise that the National Science Center recently tapped Ahl to show defense contractors and military leaders how those lessons work.
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Ahl and four of his Northwestern cadets are in Washington, D.C., this weekend preparing to lead demonstrations on Monday at the Armed Forces Communications and Electronics luncheon.
It's just another day at work for the 71-year-old career military instructor.
Ahl became interested in the Air Force in college after enrolling in ROTC at the University of Illinois. He later went through pilot training and deployed to Vietnam with an Army unit.
Upon returning, he became an instructor. He arrived at Northwestern in 1989 after retiring from active duty at Maxwell Air Force Base in Montgomery, Ala.
"I went straight, from the day I retired, here to go to work," he said.
Along with Chief Johnny Neal, Ahl teaches three, 90-minute classes of about 25 students a day.
Every high school in York County has a JROTC program, and most have more than 100 cadets. Many students spend free time working on JROTC-related activities such as competitive drill teams and model rocket clubs.
Leaders, including Ahl, stress that they're not Air Force recruiters. While students are exposed to military traditions and rules, they aren't required to serve.
Ahl runs a tight ship.
"He's very patient and very fair - although he's very strict," said Master Sgt. Larry Williams, a Rock Hill High JROTC instructor who once worked with Ahl.
Students are expected to learn the rules and follow them.
And they do.
One morning, after Ahl stepped out of class, leaving ranking cadets in charge of a study session, the room full of teens worked silently.
"If they don't progress, I don't allow them to stay in the program," Ahl said.
"My students will probably tell you that I enforce all the rules all the time, that I'm demanding. But they will probably also tell you that I provide more extra things than you can imagine."
That's true, junior Angelica Dunkle said.
"People that aren't in the corps, they'll say he's mean," she said.
But cadets know better.
Cadets can stop by during lunch or before school to watch satellite TV, use a flight simulator or play Wii - but only Wii Fit or Air Force-related games.
Students tried to talk Ahl into adding the adventure shooter game "Call of Duty," but that didn't fly.
In JROTC, students and instructors learn to be courteous at all times and address each other as "Sir" or "Ma'am."
The colonel might keep a rigid demeanor, students said, but there's room for joking and ribbing - albeit politely.
"I'll demonstrate," senior Collin Schroeder said, turning to classmate Christopher Whitt. "Mr. Whitt, I find you to be the ugliest person I've met in my life, sir."
Several plaques hang from the walls in Ahl's office listing the numerous years that his unit has been named "outstanding."
The fluorescent lights are covered with red and blue plastic wrap, because while studying psychology, Ahl learned that full spectrum lights alternating between red and blue make for a better learning environment.
That was too expensive, so he spent $15 on plastic wrap.
"Students will say it's amazing how different it feels in here than in any other classroom," Ahl said.
Ahl approaches teaching like training.
"Everything we teach, we try to make sure it has a practical application," he said. "I don't really care if you know Henry Cavendish discovered hydrogen. But I want you to know its explosive properties."
For some, his approach left a lasting impression.
"If it hadn't been for Col. Ahl, I would've probably ended up in prison," said Scott Haselden, who was a senior JROTC student in 1989. "He was strict. We clashed. I was a stupid teenager and thought I knew everything.
"Col. Ahl taught me how to get along in life. He taught me to be couth, to have tact with people."
Haselden is thankful his son Justin Medlin, a sophomore, is in Ahl's class.
"He loves it," Haselden said. "He's already got plans to go into the Air Force."