Jerôme,
According the Joe Baugher's website (
http://home.att.net/~jbaugher2/b10.html) the sale of B-10 bombers was blocked by the State Department.
From said website:
Plans to sell Martin 139s to Republican Spain were blocked by the State Department. Reports that the Martin bomber was being used in Spain on the Republican side were in error, being misidentifications of the Soviet Tupolev SB-2, which was basically similar in overall configuration.
Also interesting to read
: http://www.zi.ku.dk/personal/drnash/...ain/didnt.html
Regards,
Leendert