in how many territories were the wars fought where 280 mm mortar m1939 were used ?
SELECT DISTINCT COUNT attr_open var_uri attr_close where brack_open dbr_280_mm_mortar_M1939_ attr_open Br-5 attr_close dbo_usedInWar var_x sep_dot var_x dbo_territory var_uri sep_dot var_x a dbo_MilitaryConflict brack_close