McDonnell Douglas US Navy UDF proposals
In 1987 the US Navy announced the LRAACA competion for a new Long-Range Air Anti-submarine warfare Capable Aircraft. Douglas tendered with UDF powered versions of both the MD-87 and MD-90. Lockheed countered with an upgraded Orion model, as the P-7A. The contract was eventually awarded to Lockheed, before being cabcelled in 1990 without an aircraft being built.
The shorter fuselage and hence lighter weight of the MD-87 derived version would probably made the better choice for a dedicated ASW aircraft. Although looking awkward as a "modifed airliner", the P-3 Orion also started life as a passenger airliner.
The MD-90-based design would probably have been better served as a transport aircraft, and as such may have entered service with the Navy as the C-9D Skymaster II, taking over from the DC-9-30 derived C-9B Skytrain II.
If the contract for these aircraft had have been awarded to MDC, GE may have been able to get the engine into full production, and with a military customer, civilian operators may have been more willing to enable the MD-90 series to be built as UDF aircraft rather than as "standard" jet transports.