submarine patent
n.— «A man fought with the Patent Office for 15 years while lots of different laser products were being developed. Eventually, makers of laser products were forced to pay him. “We call those “submarine patents,” Nickey said. “When he came to the surface, he made a lot of money.”» —“OSU Could Lose Out In World Of Patents” by James W. Crowley Dispatch (Columbus, Ohio) Dec. 12, 1993. (source: Double-Tongued Dictionary)