Thread by @sebh1981

There was a plan for a DDG51 Flight III in late 1980s. In 1989, OPNAV directed NAVSEA to study an enhanced DDG51 that included a dual hangar/helicopter facilities (such as RAST that Flight I/II don't have). 1/7

This would be achieved by inserting a 40-foot section to the aft-hull to accommodate the hangars. To minimise interference of the hanger, the two after SPY-1D radar antenna was raised. Apart from that, the torpedo magazine and VLS were expanded, Mk41 VLS was increased from 2/7

96(forward 32 + aft 64) to 128 (64 +64). Flight III was with all capabilities of Flight II including combat system, towed array sonar, harpoon missiles, etc.

Flight III would have a flush deck stern, which means the main deck (01 level) was extended to stern, providing more 3/7

inner volume than previous Flight I/II that featuring lower quarterdeck at sterns.

Due to the cost, the expansion of VLS and torpedo magazine were dropped, therefore the length of the plug section was reduced from 40 feet to 28. 4/7

Due to the defense cuts when the USSR collapsed, this Flight III, which price tag was estimated 750 million more than current Flight II (per ship), was canceled by DoD in 1991.

Followed by the Flight III, OPNAV conducted another survey called Destroyer Variant (DDV) 5/7

Thus for developing a cheaper hangar-featuring destroyers, many early drafts had significant shrinkage comparing original DDG51 to achieve lower costs.

Results of DDV survey became the baseline of the current DDG51 Flight IIA, featuring a dual hangar and most of the original 6/7

Flight I/II capabilities, although some compromises were inevitable, such as removing towed array sonar, harpoon missiles and Phalanx CIWS. 7/7