cryogenic hydrogen was always the centerpiece of hydrogen powered flight. IIRC gaseous simply didn't have the right energy density to be viable. cryogenic also

cryogenic hydrogen was always the centerpiece of hydrogen powered flight. IIRC gaseous simply didn't have the right energy density to be viable. cryogenic also increased efficiency of jet engines and opened avenues for higher speeds (Tu-244 design, for example, for ~ Ma 3 supersonic transport plane)