These 'Barrage Balloons' were a cheap coastal defense against enemy planes attempting to strafe or bomb the areas inland of them. Beside the many ropes attached to them, they carried a woven steel cable anchored to the ground. Running into a cable at speed would usually shred enemy aircraft. Getting them aloft required great quantities of hydrogen gas, usually produced by pouring sulphuric acid over iron filings, a method little changed since the civil war.