Black cat commandos of the National Security Guard conducted security drills over the last few weeks to effectively secure the national capital during the upcoming Independence Day celebrations and the G20 Leaders' Summit scheduled next month, officials said on Saturday.A contingent of about 500 commandos, snipers and VIP security personnel drawn from various Central Armed Police Forces (CAPFs) have been stationed in Delhi as part of the overall protection grid being laid by the central security and intelligence setup in view of the two events.