Luftwaffe policy at this point was primarily to continue progressive attacks on London, chiefly by night attack; second, to interfere with production in the vast industrial arms factories of the West Midlands, again chiefly by night attack; and third to disrupt plants and factories during the day by means of fighter-bombers. Kesselring, commanding Luftflotte 2, was ordered to send 50 sorties per night against London and attack eastern harbours in daylight. Sperrle, commanding Luftflotte 3, was ordered to dispatch 250 sorties per night including 100 against the West Midlands. Seeschlange would be carried out by Fliegerkorps X (10th Air Corps) which concentrated on mining operations against shipping. It also took part in the bombing over Britain. By 19/20 April 1941, it had dropped 3,984 mines, ⅓ of the total dropped. The mines' ability to destroy entire streets earned them respect in Britain, but several fell unexploded into British hands allowing counter-measures to be developed which damaged the German anti-shipping campaign.