Pursuant to a congressional request, GAO reviewed the Army's development of the RAH-66 Comanche helicopter. GAO found that: (1) the Comanche's advanced capabilities, such as its avionics and targeting systems, improved engines, and lower detectability, are expected to improve the Army's ability to operate on future battlefields; (2) the distinction between the roles of the Comanche and the AH-64 Apache attack helicopter have been blurred since the advanced attack capabilities planned for the Comanche will enable it to perform the same missions and, in some cases, surpass the Apache's attack mission capabilities; (3) the Army anticipated that the Comanche would be relatively inexpensive to buy and maintain, but its unit cost in escalated dollars has increased more than 40 percent since 1988; (4) the Comanche maintenance needs could be higher than the Army's anticipated goal of 2.6 maintenance man-hours per flight hour, which would require the Army to either add maintenance staff or reduce the aircraft's planned 2,200 flying hours per year; (5) the Army continues to experience some technical risks in some of the aircraft's essential components, such as the mission equipment package and the targeting detection system, which could significantly reduce the Comanche's ability to navigate and communicate and cause the Army to incur significant additional costs; and (6) since significant developments have occurred that could affect the Comanche's requirements, such as a diminished threat, planned force reductions, and planned upgrades to other helicopters, it is an appropriate time to assess the program's viability to ensure that any future decision to buy the Comanche is appropriate.