## Facts

- DSL owned an issued patent on a “coupler mount assembly,” a clamp used to attach equipment to a railway car coupler without interfering with coupling.
- Union Switch owned a competing patent application directed to similar coupler mount assemblies.
- The PTO declared an interference between DSL’s patent (application filed Sept. 9, 1983) and Union Switch’s application (filed Mar. 27, 1984) to determine priority of invention under a single interference count.
- The interference count described a coupler mount assembly engaging specified relief holes in a railway vehicle coupler and using jaw/hook structure and a support for mounting an equipment housing.
- Union Switch asserted conception around January 1983 and actual reduction to practice no later than May 1983 based on railroad field tests of a prototype.
- Evidence showed April–May 1983 prototype testing in railroad service, including three May 1983 tests mounting the device on cabooses and carrying measurement equipment for over 700 miles at speeds above 50 mph; documentation included photographs, written reports, and recorded forces exceeding 15 g’s.
- The Board of Patent Appeals and Interferences found Union Switch proved actual reduction to practice by May 1983 and awarded priority.
- DSL filed a civil action under 35 U.S.C. § 146; the district court affirmed the Board. DSL appealed.

## Issues

1. Whether Union Switch proved an actual reduction to practice of the interference count by no later than May 1983.
2. Whether evidence of later commercial failures of devices allegedly based on Union Switch’s design undermined the May 1983 reduction-to-practice finding.
3. Whether testing on cabooses, rather than freight cars, was legally insufficient to show operability for the invention’s intended purpose.

## Decision

- The Federal Circuit affirmed the district court’s judgment upholding the Board’s award of priority to Union Switch.
- Substantial evidence supported that Union Switch built an embodiment meeting the count and tested it adequately in May 1983 to show it worked for its intended purpose.
- The court held that reduction to practice does not require the invention to be in a commercially satisfactory stage of development.
- Later commercial shortcomings did not retroactively negate an earlier, adequately supported reduction to practice.
- Testing on cabooses was not disqualifying because the count was directed to a “railway vehicle coupler” and the service tests were sufficiently rigorous to demonstrate operability.

## Legal Principles

- Actual reduction to practice requires (1) construction of an embodiment meeting all limitations of the count and (2) testing sufficient to demonstrate the embodiment works for its intended purpose.
- Commercial readiness or perfection is not a prerequisite to actual reduction to practice.
- Post hoc commercial failures or later-developed defects generally do not defeat an established earlier reduction to practice supported by credible contemporaneous testing evidence.
- The adequacy of testing is judged against the intended purpose and the scope of the count; testing conditions need not match every later commercial environment if they reasonably demonstrate operability.
- In a 35 U.S.C. § 146 action, the district court may consider additional evidence, but the challenger bears the burden to show error in the Board’s priority determination; appellate review defers to supported factual findings.

## Conclusion

The Federal Circuit left priority with Union Switch because contemporaneous May 1983 field tests showed an embodiment meeting the interference count worked for its intended purpose, and neither later commercial failures nor arguments about caboose versus freight-car conditions negated that actual reduction to practice.


DSL Dynamic Sciences Ltd. v. Union Switch & Signal, Inc., 928 F.2d 1122 (Fed. Cir. 1991)