fall upon successive prepared positions

successive barrage / successive concentration

fall upon

fall of shot calibration (fall-of-shot calibration)

successive fire concentration

be prepared to (BPT)

hastily prepared defense

Trails, Lay, Aimpoint established, Boresight verified, Safe [verification of lay], Prefire checks performed, Ammunition Prepared

specially prepared land site

prepared air

well-prepared defenses

fire at/on/upon (smb./smth.)

upon completion

achieve an agreed-upon outcome

lie upon one's arms

wreck destruction (upon)

detonate upon impact

assault of fortified positions

key positions

priority of positions

betray the positions

initial tactical deployment positions

disengaged positions

ammunition at gun positions

line of the forward positions

reconnaissance for positions

avenues of approach within the hostile positions

within the hostile positions

rush enemy positions

settled into positions

mark out defense positions

angle of fall

fall of the hammer