State tort claims are pre-empted where the plaintiff’s injury is caused by the allegedly defective design of military equipment manufactured by the defendant pursuant to a contract with the federal government. Boyle v United Technologies Corp., 487 U.S. 500 (1988). This case established the government contractor defense to tort liability. The Court reasoned that although state tort law may allow products liability claims against military manufacturers, this is an area of uniquely federal concern, regardless of the lack of federal legislation specifically claiming the immunity the absence. In an effort to determine the scope of this defense, the Court stated that this pre- emption is limited to areas of "significant conflict" between federal policy and state law. For guidance on the extent of "significant conflict", the court applied the discretionary function exception of the FTCA, which is to say that state law will be pre-empted wherever it threatens a discretionary function of the federal government. Here, the design of the allegedly defective product was a military discretionary decision.

In sum, Boyle established that state law which imposes liability on a military manufacturer is pre-empted when (1) the US approved reasonable precise product specifications, (2) the equipment conformed to those specifications, and (3) the supplier warned the US of the known dangers of using the equipment.

An important issue is whether the defense applies only to contracts with the military, or whether it can be used by other government contractors. The Supreme Court has employed language hinting that it may apply to all contractors, but has never spoke directly on the issue. See Hercules, Inc. v. U.S., 516 U.S. 417, 421 (1996) ("The Government contractor defense . . . shields contractors from tort liability for products manufactured for the Government in accordance with Government specifications, if the contractor warned the United States about any hazards known to the contractor but not to the Government"). The lower federal courts are split on the issue.

Courts that favor applying the defense to non-military contractors include the Western District of Wisconsin, Western District of Kentucky, District Court of Maryland, Southern District of Mississippi, District of South Carolina, and District Court of New Jersey. These courts apply the Boyle analysis.