Laydown delivery

Laydown delivery is a mode of deploying a free-fall nuclear weapon in which the bomb's fall is slowed by parachute so that it actually lands on the ground before detonating. Laydown delivery requires that the weapon's case be reinforced so that it can survive the impact, and generally involves a time-delay fuse to trigger detonation. Laydown mode can be used to increase the effect of the weapon's blast on built-up targets such as submarine pens, or to transmit a shock wave through the ground to attack deeply buried targets. An attack of this type produces large amounts of radioactive fallout.

It has the additional advantage of allowing the carrier aircraft to fly very low and still get away without being destroyed in the detonation. This is particularly important where high-yield nuclear weapons such as the B41 and B53 nuclear bombs are concerned. The low altitude delivery also helps hide the aircraft from surface-to-air missiles. It was for this reason that laydown was selected for the Vickers Valiant bomber of the Royal Air Force, as this design became increasingly vulnerable to Soviet weapons, especially the SA-2 missile. Laydown was referred to as "Equipment 2 Foxtrot" in RAF parlance, with Echo referring to toss bombing and Hotel to a particular climbing delivery method used by the Avro Vulcan.

ICT 1301

The ICT 1301 and its smaller derivative ICT 1300 were early business computers from International Computers and Tabulators. Typical of mid-sized machines of the era they used core memory, drum storage and punched cards, but they were unusual in that they were based on decimal logic instead of binary.

The 1301 was designed by an ICT and GEC joint subsidiary, Computer Developments Limited (CDL) at GEC's Coventry site.

The 1301 was the main machine in the line. Its main memory came in increments of 400 words of 48 bits (12 decimal digits) plus two parity bits. The maximum size was 2,000 words. It was the first ICT machine to use core memory.

Backing store was magnetic drum and optionally one inch, half inch or quarter inch wide magnetic tape. Input was from 80 column punched cards and optionally 160 column punched cards and punched paper tape. Output was to 80 column punched cards, line printer, and optionally to punched paper tape.

The machine ran at a clock speed of 1 MHz and its arithmetic logic unit (ALU) operated on data in a serial-parallel fashion—the 48-bit words were processed sequentially four bits at a time. A simple addition took 21 clock cycles; hardware multiplication averaged 170 clock cycles per digit; and division was performed in software.

ICT 1900 series

ICT 1900 was the name given to a series of mainframe computers released by International Computers and Tabulators (ICT) and later International Computers Limited (ICL) during the 1960s and '70s. The 1900 series was notable for being one of the few non-American competitors to the IBM System/360, enjoying significant success in the European and Commonwealth markets.

Creation of the ICT 1900 series

In early 1963 ICT was in negotiations to buy the computer business of Ferranti. In order to sweeten the deal Ferranti demonstrated to ICT the Ferranti-Packard 6000 (FP6000) machine, developed by its Canadian subsidiary Ferranti-Packard.

The FP6000 was an advanced design, notably including hardware support for multiprogramming. ICT considered using the FP6000 as their medium-sized processor in the 1965–1968 timeframe, replacing the ICT 1302. Another plan being considered was to license a new range of machines being developed by RCA, probably compatible with the expected IBM 8000.

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