Sentence:  The weekly loss is partly counterbalanced by 500 arrivals each week from West Germany , but the hard truth , says Crossman , is that `` The closing off of East Berlin without interference from the West and with the use only of East German , as distinct from Russian , troops was a major Communist victory , which dealt West Berlin a deadly , <WSD>possibly</WSD> a fatal , blow . 
Meaning of the word marked with <WSD> tags:  by chance