Following the success of the Collier and Beale built trial-production sets the production of 1000 sets was authorised. However, considerable difficulty was experienced in obtaining certain components, especially meters and by April 1942 only sufficient material for the manufacture of 750 sets of the 1000 sets authorised was available.
The ongoing lack of meters forced a minor redesign during the first production run so that only one meter was required. The redundant meter hole left in the remaining stock of already manufactured front panels was covered with a metal plate fitted with a watch holder. Sets manufactured with this modification became known as the Mk-1 type 2. Less than 1000 of this type were made.