α-β titanium alloys are used in armor plate applications due to their capability to defend aga inst ballistic threats while having a 40% lower density than steel. ATI 425® was developed as a cold-deformable alternative to Ti-6Al-4V with similar ballistic properties and improved blast performance owing to the alloy’s higher damage tolerance. ATI Titan 27™ is an evolutionary step forward on ATI 425” Alloy, and is being developed as a higher-performance titanium armor alloy owing to its greater than 10% improvement in strength with similar ductility and formability. Recent work has demonstrated a novel deformation mechanism that explains the improved cold deformation observed in both alloys over Ti-6Al-4V. This mechanism, a twinning of a-phase coinciding with slip in the B-phase, is unique among high-strength titanium alloys. Moreover, twinning is well known to be suppressed with high oxygen content, and ATI Titan 27™ Alloy has one of the highest oxygen targets across high-strength α-β titanium alloys. Mechanical properties and ballistic results of ATI Titan 27™ Alloy will be covered, as well as results from an in-situ microscopy deformation study demonstrating the slip-twinning mechanism. Typical results for ATI Titan 27™ will be compared to the ATI Ti-6AL-AV alloy, of which ATI has manufactured more than 16 million pounds for armor plate.