(i) Correct Runs, where incorrect runs had been done before.
(ii) More runs, runs with spanning etc.
(iii) Motor and Psi runs, either immediate or delayed. Messages set on all chis
before motors were broken were de-chied, but those set strongly on some chis
only, were held for 'delayed motor runs'.
(iv) 4-wheel runs (see 23H(c)). These were done on long messages for which normal
methods gave no result, if and when there was machine time to spare.
(v) Runs on a Doctored tape i.e. a tape altered to counteract a message slide
discovered by spanning on Colossus.
In all cases it was best for the D.O. to write out quite precisely what he
wanted done. As it was often necessary for the D.O. to calculate the expected
score of a motor run in order to decide if it was worth while, many motor runs
were issued with E.S. worked out.
Further runs fell naturally into two categories: Runs strongly expected to
succeed and runs done because insufficient work had been done to justify
abandoning. The first category was marked so that the R.R. could give it suitable
(e) Hut 3 Priority Messages
When Hut 3 believed that messages were of special urgency, the C.O. was sent
a chit, requesting that it should be marked Z, ZZ, or ZZZ. If the tapes had not
been set the request was passed to the D.O. and Logs Registrar. All documents
were marked with the priority sign and treated specially. If other work was
plentiful, Z and ZZ messages were run rather more fully than other tapes. If
already abandoned when the request arrived, a rewrite was ordered, and run fully.
4-wheel runs were not done. ZZ had priority over Z. ZZZ priority was only
ordered in special cases. All possible runs including 4-wheel runs were done at
once on the first tape and a rewrite was ordered. All runs including 4-wheel runs,
were repeated on the rewrite.
(f) Routine checks for machines
(i) Chi test runs and tapes
Before the first de-chi on a new key day was ordered by the T.R., a chi test
tape was ordered from Tunny. This was sent to a Colossus on which the new chis
had been set up, and chis and test tape were checked against each other by adding
them together. Test Runs were then done on this Colossus and one other, and if
they agreed several copies were made and stuck in each Colossus wheel book.
(ii) Psi rest Runs and Tapes
Psi test tapes were made (with suitable limitation) as soon as psis and
motors were known. The routine and uses of psi test runs and tapes were similar to
those for chi test runs and tapes.
(iii) Routine Tests.
A routine test (using a general test tape) was carried out on two Colossi
per shift. The test took about 20 minutes and was done by Wrens specially trained
by the Engineers.