Opinion of the Court BOOTH, Chief Justice, delivered the opinion of the court: The plaintiff is now in the Corps of Engineers, United States Army. He was prior to May, 1917, an employee of the defendant on the Mississippi River Commission, having held this position for a period of seven years. Under the provisions of the act of June 25, 1910, 36 Stat. 851, as amended by the act of July 1, 1918, 40 Stat. 705, conferring jurisdiction upon this court in patent cases, the plaintiff, a patentee, is precluded from bringing suit against the defendant for an alleged infringement of his patent rights, because of his service in the Government at the time he makes his claim. A proviso to the foregoing acts so states. The Congress enacted the special jurisdictional act, set out verbatim in finding 2. This act was approved by the President on December 17, 1930, and the present suit for infringement was commenced January 16, 1932. The parties to the case agree that the special jurisdictional act confers jurisdiction upon the court to adjudicate the case irrespective of plaintiff's service in the Government and the statute of limitations, but seriously disagree as to the scope and meaning of the act in other respects. The special act contains a number of specific and mandatory provisions imposing upon the court a method of procedure in adjudicating the issues, and it is these provisions which originate an interposed defense vital to the determination of a governmental liability for any infringement of plaintiff's letters patent. The plaintiff takes the position that the express waiver of governmental service and the statute of limitations places the litigation in the same status as any other ordinary patent case, and that the additional express provisions of the act exacting consideration of governmental service, expenditure of Government funds in developing the inventions, etc., have exclusively to do with fixing the amount of compensation due in the event of a determined infringement of the patents. Plaintiff's letters patent 1173879, relating to a revetment structure, were issued February 29, 1916, and on this date the patentee was an employee of the Mississippi River Commission, serving as junior engineer and chief of a revet Opinion of the Court ment party. On the same date letters patent 1173880 were issued to plaintiff relating to a molding frame for casting the revetment structure described in patent 1173879. Infringement of this patent is no longer claimed in this suit. On June 5, 1917, the date when letters patent 1229152 for a launching apparatus were issued to plaintiff, he was a member of the Engineer Corps of the United States Army, having been commissioned as such about May, 1917. Knowledge by Congress of the facts just stated, and of additional ones to be stated, was undoubtedly the reason for inserting the provisions of the special jurisdictional act which it is essential to quote. They are as follows: In determining whether or not said David McD. Shearer is entitled to compensation and the amount of compensation, if any, for the use of said inventions the court shall take into consideration, if and so far as the facts may warrant, the facts, if proved, that while said David McD. Shearer was engaged in perfecting the invention he was in the service of the United States as a junior engineer superintendent in charge of willow bank revetment construction under the Mississippi River Commission, and whether and, if at all, to what extent said inventions or any of them were discovered or developed during the working hours of his Government service, and to what extent his said inventions for protection of river channels and banks differ from the methods previously used, in material, method of laying, permanency, and value, and, whether if at all to what extent the expense of making experiments, trials, and tests for the purpose of perfecting said inventions was paid by the United States, and if any such expense was incurred by the United States, whether and, if at all, to what extent the United States received compensation for such expense. We think claims (3) and (6) of patent 1173879 and claims 6, 8, and 9 of patent 1229152 are valid and read upon the revetment apparatuses used by the Government. This fact does not however determine the defendant's liability as for an infringement of the same. The above quoted provisions of the special jurisdictional act considered in connection with the provisions of the entire act are of paramount importance in the ascertainment of governmental liability as claimed. 109870-39-c.c.-vol. 87- -7 Opinion of the Court The plaintiff was for about seven years employed, as previously observed, as junior engineer and chief of a revetment party by the Mississippi River Commission, a governmental agency. During this entire period the adopted method of the Commission in revetment work was to utilize what is termed fascine mattresses. Fascine mattresses were made up of willow brush obtained near the banks of the river. The willow brush was segregated into bundles about 8 feet long and 12 inches in diameter, compressed tightly and wired together at intervals. When the willow mattress was completed it resembled a raft, and after being launched floated upon the surface of the river. To accomplish its submergence at a desired point in the river bed the willow float would be weighted down by placing thereon a stone ballast consisting of large sized pieces of stone capable of being carried by a single workman. The plaintiff was thoroughly familiar with the process of constructing, launching, and sinking fascine mattresses and their value when placed in retarding erosion of both the banks and beds of the stream. He had supervised about seventy installations of fascine mattresses. During the course of his extended experience in revetment work the imperfections of fascine mattresses to accomplish all that was desired became apparent to him. Being an engineer of ability he observed that fascine mattresses were of comparatively short life, that the cables which held them together yielded to rust, and upon their disintegration were readily susceptible to misplacement, exacting numerous replacements, and this was especially true with respect to subaqueous revetment work. November 25, 1913, Major Woodruff, plaintiff's superior on the River Commission, addressed an order, the contents of which reached the plaintiff, calling attention to the "Failure of bank revetments" along the banks of the Mississippi River and directing the chiefs of all revetment parties to submit on or before April 1, 1914, their ideas as to the cause of said failure, and their suggestions as to essential changes in the methods of construction employed. The plaintiff on or about February 12, 1914, responded to the above order and in his report entitled "Sketches Opinion of the Court showing Failures and Recommended Revetment Types" proposed the use of concrete as a substitute for riprap then used in upper bank protection. The record sustains an inference that at this time plaintiff was interested in the use of concrete in revetment structures. We say this because plaintiff's proposal, while it referred especially to upper bank protection, also contained a reference to subaqueous willow mat protection, noting its imperfections, and indicating that the willow mat was good "as long as it lasts", and closing with an observation that in any event it was superior to ever-failing riprap. In May, 1914, plaintiff was on leave of absence and at his home in Lufkin, Texas. His interest in the use of concrete in revetment structure continued, and he communicated with the district office of the Third Mississippi River District, and among other things asked for authority to investigate further the subject matter under consideration. Major Slattery, plaintiff's superior officer, willingly acceded to plaintiff's request, commended him for his report, and gave him plenary authority to study and report upon improved methods pertaining to the work in which they were engaged. On some indefinite date, but at least as early as October 6, 1914, plaintiff submitted to the District Engineer Officer of the proper district what is identified in the record as plaintiff's exhibit 7. This exhibit is important; it is made up of detail drawings accompanied by a meticulous and lengthy description disclosing the method of constructing concrete mats and mattresses, an apparatus for their molding, and a mechanism for their launching, together with a discussion as to their availability for subaqueous revetments instead of fascine mattresses. The plaintiff testifies and now contends that he conceived the apparatuses disclosed in exhibit 7 and prepared the exhibit itself outside his regular working hours. The defendant challenges the fact and insists in addition that what the plaintiff did was within his duties and in pursuance of the orders of his superior officer. On the date he forwarded exhibit 7 to the district office he was not upon an active duty status, being away on his vacation, Opinion of the Court and plaintiff is the only witness testifying to the date when he conceived the drawings and apparatuses disclosed by exhibit 7. Courts are loath to accept the uncorroborated testimony of a plaintiff as to this point. We think, however, that exhibit 7 in this particular instance furnishes the corroboration. Eibel Process Co. v. Paper Co., 261 U. S. 45; Symington Co. v. National Castings Co., 250 U. S. 383. The next important proceeding was inaugurated in April, 1915. Major Slattery notified the plaintiff of the Commission's purpose to conduct a trial of the concrete revetment structure disclosed by him. To accomplish this act it was necessary to alter the mechanism used to launch fascine mattresses and plaintiff received express instructions to be present and supervise this work. Plaintiff was present and did personally supervise all that was done until June 28, 1915, on which date he was relieved of this assignment and transferred to other duties. In July, 1915, a number of attempts were made to launch and place concrete revetments in accord with plaintiff's disclosures. Concrete mats were cast and formed into sections and some of them were successfully launched. This trial however demonstrated difficulties of a serious nature in the launching apparatus, so serious that upon one attempt the entire concrete mattress went overboard and was lost. The necessity for changes in the launching apparatus was apparent and imperative. The plaintiff was present during this demonstration and while he took no official part in it his expenses were paid for attending it. This is known as the Greenville test. In August, 1915, plaintiff submitted to Major Slattery a blueprint disclosing his modified design intended to correct and overcome the imperfections of the launching apparatus used at Greenville. Plaintiff some time prior to this date had resumed his official duties at Vicksburg. This modified design was not immediately tested. The Commission lacked available appropriations to do so. Early in 1916 plaintiff's modified design of the launching apparatus was constructed under his personal supervision and subjected to a trial at Delta Point in July, 1916. The record discloses that this trial was more successful than the |