He followed the Operations track, originally specializing in Engineering, which he took for one semester, then transferred to Tactical Operations. He made the Academy's Red Squad his third year.

After graduating the Academy, he was an ensign on the U.S.S. Condor for two years. While on the Condor, he was instrumental in solving an incident at the colony on Fremoria. The colonists were being attacked by an indigenous quadripedal race. Analyzing the threat, Krol realized that the colony was built on the only area of the planet that would support the race's peculiar den habits. He brought this to the attention of the colony director, who had the colony moved immediately with the old colony dismantled. Krol received a commendation for finding the best solution with the least possible casualties for both sides.

This was also the cause of his promotion to Lieutenant Commander and transfer into special forces, and eventual posting on the U.S.S. Sunfire. During his time aboard the Sunfire, he rose to the rank of Lieutenant Commander. When the Sunfire was drydocked for a refit, he was transferred to the U.S.S. Heisenberg.

He had only been on the Heisenberg a short time when, on an away mission, his team of three was trapped in a cave-in. One of the team, an ensign, was severely wounded and near death. Communicators were ineffective due to a freak ion storm in the upper atmosphere, and there wasn't enough air in the cave for the team to wait it out. With the other team member, a lieutenant in the medical field, tending the wounded ensign, Krol personally dug through 30 metric tons of rock to free them from the cave. Upon their return to the ship, the ensign was taken into surgery, but suddenly went into a cardiac arrest and died before the procedure could begin. Krol received an award for heroism and was promoted to the rank of commander. He still felt that the death of the ensign was a blemish upon his honor, though, and has strived to regain that honor by going even more above and beyond.

Once promoted to commander, he was transferred to the U.S.S. Washington to serve as Executive Officer and his uniform was changed from Operations Gold to Command Red.

A surprisingly short time after being put on the Washington, a new ship was created, the U.S.S. Potomac. Krol was offered command of the fine ship, and he accepted. Upon his acceptance, he was promoted to the rank of Captain. Not too long after accepting the Potomac, she gained sentience, and was destroyed while holding the crew aboard her against their will. After the destruction of the Potomac, the crew was rescued by the U.S.S. Kriemhild and taken to Starbase 47, where they were given the new ship, the U.S.S. Minerva.