Disclaimer: Infrared is maybe the wrong term, I took it to mean anything that we do not currently perceive with a longer wavelength than what we see as red. I don't think in the following they refer to "seeing any light with long wavelengths".
I encountered a fourth-hand claim of army experiments to give humans infrared vision a while ago. He quotes in full from a textbook (Sekuler, R., and Blake, R. (1994). Perception (3rd ed.). Springfield, Ill.: Thomas.) pp. 62-63:
The following story dramatizes how photopigments determine what one can see. During World War II, the United States Navy wanted its sailors to be able to see infrared signal lights that would be invisible to the enemy. Normally, it is impossible to see infrared radiation because, as pointed out earlier, the wavelengths are too long for human photopigments. In order for humans to see infrared, the spectral sensitivity of some human photopigment would have to be changed. Vision scientists knew that retinal, the derivative of vitamin A, was part of every photopigment molecule and that various forms of vitamin A existed. If the retina could be encouraged to use some alternative form of vitamin A in its manufacture of photopigments, the spectral sensitivity of those photopigments would be abnormal, perhaps extending into infrared radiation. Human volunteers were fed diets rich in an alternative form of vitamin A but deficient in the usual form. Over several months, the volunteers' vision changed, giving them greater sensitivity to light of longer wavelengths. Though the experiment seemed to be working, it was aborted. The development of the "snooperscope," an electronic device for seeing infrared radiation, made continuation of the experiment unnecessary (Rubin and Walls, 1969). Still, the experiment demonstrates that photopigments select what one can see; changing those photopigments would change one's vision.
The second-hand source is cited 4 times according to Google Scholar, so apparently some people had access to it (or were unscrupulous about scraping references from another textbook...). But in the one citing paper I have access to, they cite it for a different claim.
On a Wikipedia talk page about infrared vision, this Snopes report was considered relevant. While the claim is much more crude and about Britain's airforce instead of the US navy, it does have some similarities.
Lundquis states himself he couldn't get his hands on the second-hand source, so we don't know the authors of the first study. I tried finding it via Google too (a while ago) and didn't succeed. I don't know how navy experiments are published (delayed maybe?!), so that was a probable hindrance.