 During the entire period of 1970 – 74 , FRELIMO intensified guerrilla operations , specialising in urban terrorism . The use of landmines also intensified , with sources stating that they had become responsible for two out of every three Portuguese casualties . During the conflict , FRELIMO used a variety of anti @-@ tank and anti @-@ personnel mines , including the <unk> ( Black Widow ) , <unk> @-@ 46 , and <unk> . Even amphibious mines were used , such as the <unk> . Mine <unk> , an acute fear of landmines , was rampant in the Portuguese forces . This fear , coupled with the frustration of taking casualties without ever seeing the enemy forces , damaged morale and significantly hampered progress . 
