These were German wire-guided missiles.
The first to be developed was the X4, an air-to-air missile, work on which began
in June 1943.
It was a finned missile with a wingspan of 6ft 6in, driven by a BI-fuel liquid
rocket at 550mph. Bobbins of wire were carried in the wing tips, which unwound
as it flew, and guidance signals were sent down the wire to function spoiler
tabs on the wing surfaces which caused it to alter direction.
The warhead carried 44lb of explosive and a "Kranich" acoustic proximity fuze.
Prototypes were flown successfully in September 1944 but the wire link from
aircraft to missile was considered too restricting, and work then began on two
alternative versions, one using the 'Pudel' acoustic homing system in which the
missile would find its own way to the noise of the targets engines, and one
using a radio link system of guidance. Neither of these had passed the
development stage when the war ended. As an offshoot of the X4 program. it was
decided to develop a wire-guided ground-to-ground missile for antitank use; this
became known as the X7. It was gyro-stabilized and wire-guided in the same
manner as the X4 but carried a hollow charge warhead fitted with an impact fuze.
It was propelled by a two-stage solid propellant rocket motor, weighed 22lb, had
a range of 1000 meters and could penetrate over 200 mm of armour. The X-series
were developed by the Ruhrstahl AG company of Düsseldorf, but none was ever
brought to sufficient perfection to begin production before the war ended.
Nevertheless, the company deserve recognition for being the originators of the
wire-guided antitank missile which is today in the armories of every nation,
and, except for relatively small refinements, is made to the same specifications
as the X7.