In the book The Coming Energy Revolution, author Jeane Manning reports that some "free energy" inventors may have been silenced by the US Government. Jeane Manning writes
If you were an inventor trying to patent an important new-energy discovery, you might receive a secrecy order along the lines of the one reproduced here. According to information obtained under the Freedom of Information Act by the Federation of American Scientists, the Pentagon placed 774 patent applications under secrecy orders in 1991--up from 290 in 1979--and 506 of these orders were imposed on inventions by private companies. The government has standing gag orders on several thousand inventions. The following order, issued in the 1980s, was obtained by inventor Ken MacNeill of Georgia and revealed in 1983.
NOTICE: To the applicant above named, his heirs, and any and all his assignees, attorneys and agents, hereinafter designated principals.
You are hereby notified that your application as above identified has been found to contian subject matter, the unauthorized disclosure of which might be detrimental to the national security, and you are ordered in nowise to publish or disclose the invention or any material information with respect thereto, including hitherto unpublished details of the subject matter of said application, in any way to any person not cognizant of the invention prior to the date of the order, including any employee of the principals, but to keep the same secret except by written consent first obtained of the Commissioner of Patents, under the penalties of 35 U.S.C.  182, 186.
Any other application already filed or heteafter filed which contains any significant part of the subject matter of the above identified application falls within the scope of this order. If such other application does not stand under a secrecy order, it and the common subject matter should be brought to the attention of the Security Group, Licensing and Review, Patent Office.
If, prior to the issuance of the secrecy order, any significant part of the subject matter has been revealed to any person, the principals shall promptly inform such person of the secrecy order and the penalties for improper disclosure. However, if such part of the subject matter was disclosed to any person in a foreign country or foreign national in the U.S., the principals shall not inform such person of the secrecy order, but instead shall promptly furnish to the Commissioner of Patents the following information to the extent not already furnished: date of the disclosure, name and address of the disclosee, identification of such part; and any authorization by a U.S. Government agency to export such part. If the subject matter is included in any foreign patent application or patent this should be identified. The principals shall comply with any related instructions of the Commissioner.
This order shall not be construed in any way to mean that the Government has adopted or contemplates adoption of the alleged invention disclosed in this application; nor is it any indication of the value of such invention.