DHS's commitment to the development of a counter-MANPADs system was largely spurred by a terrorist launching of surface-to-air missiles at an Israeli airliner departing from Mombasa, Kenya. The objective of the DHS program is to migrate existing military countermeasure technologies to the civil aviation environment and to minimize the total life-cycle cost of the system, which includes, development, procurement, installation, operation, and support costs. The solicitation focuses primarily on the DIRCM concept, which combines a missile warning system (MWS) to detect a missile launch and a laser to jam the guidance system of the missile. The challenges posed in adapting a military counter-MANPADS system to commercial aircraft include establishing system requirements, maturing technology and design, and setting reliable cost estimates; e.g., DHS must account for a wide variety of aircraft types in designing and integrating the system. GAO's past work on the best practices of product developers in government and industry has found that the use of a knowledge-based approach is a key factor in successfully addressing such challenges. This approach includes the use of exit criteria or controls to ensure that sufficient knowledge has been attained at critical phases of the product development process. Based on the input that GAO provided during the course of its review, DHS updated its initial solicitation to incorporate these knowledge-based exit criteria. GAO recommends that the Secretary of Homeland Security ensure that the knowledge-based approach is fully implemented throughout the course of the counter-MANPADS development program.