Trench works, villages, firebases, headquarters, bunkers and gun emplacements provide strategic options for players. PAVN responded by increasing its daily artillery bombardments of the firebases, notably Lolo and Hope. On 14 December Firebases Alpine, Argonne and Gurkha were closed. Several small firebases were overrun within hours. FSB Mary Ann's construction was no different from many other U.S. firebases in South Vietnam. The attacks on the firebases continued as April wore on. In addition ARVN Airborne and Rangers occupied a string of firebases along Rocket Ridge. Ironically, the very efficiency and convenience of firebases, could at times aid VC/NVA forces. Between 15 and 20 May, Firebases Bastogne and Checkmate were recaptured. Firebases could also be "leapfrogged" or shifted in response to an advance or operational needs.