Once per game, declared at the start of any close combat phase, Althran and all friendly units with the Martial Prowess special rule within 6" of him gain +1 To Hit for the duration of that phase.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
Once per game, declared at the start of any close combat phase, Althran and all friendly units with the Martial Prowess special rule within 6" of him gain +1 To Hit for the duration of that phase.