Until recent changes in U.S. patent law, patent applications were not published until 18 months after filing, as was and is the case in other patent systems. As a result, by deft filing of divisionals, continuations, and CIPs, followed by abandonment of the original application, a patent applicant could keep a patent secret for decades, allowing it to surface as a patent only when an industry using the technology had evolved. Typically, the applicant also used the CIP process to steer the claims in the direction of industry trends. Further complicating this activity was the fact that U.S. patent terms used to be measured from the issue date of the patent (seventeen years) rather than from the application date.
The most notorious user of submarine patents was the late Jerome Lemelson, who, with patents that appeared to cover bar codes, extracted over $1 billion in royalties before the patents were found unenforceable and indeed not enabling. The last few submarine patents are now expiring.