It should go without saying in the aerospace engineering and development world that complex flight systems should be thoroughly tested before being pressed into production and service, but U.S. missile defense programs have been exempted from this axiom.

As noted in a recent U.S. Government Accountability Office (GAO) report, a number of high-profile missile interceptors have entered production while still undergoing testing, an overlap attributed to aggressive and unrealistic deployment schedules. As a result, according to the congressional watchdog agency, these systems have required retrofits that have halted production, driven up costs and compromised performance.

Programs afflicted by so-called concurrency issues include the Ground-based Midcourse Defense system, the primary U.S. territorial missile shield; and upgrades to the sea-based Standard Missile (SM)-3, the cornerstone of U.S. plans to defend Europe against missile attacks. Both programs have had aggressive deployment schedules dictated by presidents.

To be clear, the GAO has not uncovered anything here that hasn’t been flagged before. In February 1998, for example, an expert panel led by retired Gen. Larry Welch, former Air Force chief of staff, who at the time was the head of a trusted Pentagon think tank, warned that U.S. missile defense systems were being inadequately tested due to unrealistic development schedules driven by a perceived “urgency of the need.” The report coined the oft-repeated phrase “rush to failure” in characterizing flight-test programs conducted with a view toward demonstrating deployment readiness rather than learning about the system being flown.

Similar themes were later adopted by critics of former U.S. President George W. Bush’s missile defense policy, spelled out in 2002, which called for deploying a limited capability to defend the U.S. homeland in the 2004-2005 timeframe.

In its report, the GAO provided fresh evidence of the pitfalls of running crash development programs. The initial interceptors for the Ground-based Midcourse Defense system, for example, required “extensive and expensive” retrofits that are still under way. A similar retrofit requirement halted production of an enhanced version of the interceptor, dramatically inflating its cost — from $236 million to $1 billion to confirm its capability — while adding several years to its schedule, the report said.

Concurrency is also an issue on various SM-3 upgrade programs, the GAO said, noting that the U.S. Missile Defense Agency (MDA) has tentative plans to commit to full-scale development of the SM-3 Block 2B interceptor more than a year before preliminary design review. “By contrast, major defense acquisition programs outside MDA are generally required to complete this review before committing to product development,” the report said.

Indeed, MDA programs have long been accorded this sort of special treatment, in part because of the unsettling proliferation of ballistic missiles in unfriendly corners of the world. The idea of protecting otherwise defenseless U.S. cities, deployed forces and allies has undeniable political appeal even if, as North Korea’s latest failed missile launch attests, the immediacy of the threat to the U.S. homeland is often overstated.

Staunch missile defense advocates have argued that it is better to have unproven defenses than nothing at all, but the GAO makes a stronger case that rushing systems into production and service is counterproductive. Here again, the Welch report proved prophetic: “The virtually universal experience of the study group members has been that high technical risk is not likely to accelerate fielded capability. It is far more likely to cause program slips, increased costs, and even program failure.”

Indeed, the importance of missile defense is a dubious justification for dispensing with proven engineering discipline and development practices, including rigorous testing. If anything, the opposite is true. The MDA’s quickest path to deploying credible, effective missile defenses that don’t break the bank — the Pentagon is in no position these days to squander resources — is by mapping out program plans and schedules that match available budgets and resisting the temptation to cut corners.