The McLachlan passage Block quotes uses an 'E' grade, in tension with Block's own 'A1 to D5' description of the wartime scale

admiralty-codegodfreymclachlansametverificationunverified

Ludo Block quotes, from p. 23 of McLachlan's Room 39, an officer describing a source whose reliability "will be 'C', 'D', or even 'E'" on the U-boat's operational area. If Block transcribed accurately, a fifth reliability letter was in use in the wartime scheme. That sits awkwardly with Block's own summary of the scale as running "from 'A1' to 'D5'" (four letters, five numbers). Either the summary is loose, or the wartime scale was not the narrow A–D form.

This bears on a specific inference in claim-godfrey-1939-devised-admiralty-codes-two-axis-grading-to-fix-report-anarchy: that the range "widened at some point between 1939 and its modern codification." With an E already in a McLachlan-attributed passage, that inference has no sourced footing. The later doctrinal scale is A–F / 1–6 (claim-admiralty-code-grades-sources-on-two-independent-axes); Samet's 1975 paper cites it to US Army FM 50-5 (1971) and dates nothing earlier than "many years" of use (claim-samet-1975-argued-for-more-rating-categories-not-fewer), so it does not settle the question either. See also claim-block-2021-attributes-only-intolerable-to-mclachlan-room-39-p22 for how little of Block's page is McLachlan's own text.

Verification: question-verify-godfrey-nid-origin-against-mclachlan-room-39.