Christopher Johansen was an officer and WWII veteran.
Johansen was a friend of the Scully family while Dana Scully grew up. He lost touch later in life though and was not aware of William Scully's passing. Johansen's son was killed during training in Gulf War.
Johansen served as the executive officer of the Zeus Faber in WWII under Kyle Sanford. When the ship was ordered and successfully found wreckage of a squadron of planes, the ship detected a Japanese destroyer nearby. Unbeknownst to Johansen, the downed squadron shot down a UFO and black oil from it had infected the captain, who began to behave irrationally and refused to retreat from the area. Johansen objected to the decision and finally decided to lock the captain in with much of the badly radiated crew inside. He ordered the ship to leave for home. After the ordeal, Johansen never got an explanation as to what happened.
In 1995, Scully visited Johansen at Miramar base and asked him his recollection of certain related aspects and phrases, collected as part of the investigation into the Piper Maru. Johansen pretended not to remember the answers, though told the base guards to detain her when she left so he could discretely talk to her. Coloring his experience with noting they "bury the dead alive," he explained what he knew, which was that he was sent to find the squadron which had a nuclear bomb in it. (TXF: "Piper Maru")