{"id":604,"date":"2025-03-28T22:21:29","date_gmt":"2025-03-28T21:21:29","guid":{"rendered":"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/?page_id=604"},"modified":"2025-04-17T17:31:09","modified_gmt":"2025-04-17T15:31:09","slug":"history","status":"publish","type":"page","link":"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/index.php\/m-138\/history\/","title":{"rendered":"History"},"content":{"rendered":"\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong><span style=\"text-decoration: underline;\">Genesis of the M-138<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<p class=\"has-text-align-left wp-block-paragraph\">In the 1920 and early 1930s, the field cipher device widely used by the U.S. Army was the M-94. However, its alphabets were stamped on aluminium discs which could not readily be replaced.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Late in 1933 the Army, recognizing the added security of being able to easily change alphabets, devised plans  for a replacement device.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\"><\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<p class=\"wp-block-paragraph\">Several systems were designed:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The M-136, invented by William F. Friedman, was a cylindrical device similar to the M-94 with 25 discs but with alphabets printed on papers strips attached around the discs. This device turned out not to be practical and only one model was ever built.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"636\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-1024x636.jpg\" alt=\"\" class=\"wp-image-608\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-1024x636.jpg 1024w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-300x186.jpg 300w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-768x477.jpg 768w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-1536x954.jpg 1536w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m136-2048x1273.jpg 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>M-136 cipher device &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<ul class=\"wp-block-list\">\n<li>The M-137 was invented by U.S. Navy Lieutenant Smellow. It was a board, supported at 45\u00b0 by a frame, on which paper strips slide in an endless loop. It was used by the Navy for 3 years.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"1015\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137-1024x1015.png\" alt=\"\" class=\"wp-image-609\" style=\"width:auto;height:300px\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137-1024x1015.png 1024w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137-300x297.png 300w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137-150x150.png 150w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137-768x761.png 768w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m-137.png 1458w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>M-137 cipher device &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<ul class=\"wp-block-list\">\n<li>As these were unsatisfactory for the Army 3 experimental models (M-138-T, M-138-T2, and M-138-T3) were designed based on a strip cipher device invented in 1915 by U.S. Army Captain Parker Hitt, and tested simultaneously.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"383\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-1024x383.png\" alt=\"\" class=\"wp-image-611\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-1024x383.png 1024w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-300x112.png 300w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-768x287.png 768w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-1536x575.png 1536w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t3-2048x766.png 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>M-138-T3 cipher device &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<ul class=\"wp-block-list\">\n<li>M-138-T2, found to be the most satisfactory, was refined into M-138-T4 (no M-138-T2 remains, as they literally became the M-138-T4).<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"763\" height=\"1024\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t4-763x1024.png\" alt=\"\" class=\"wp-image-612\" style=\"width:auto;height:350px\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t4-763x1024.png 763w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t4-223x300.png 223w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t4-768x1031.png 768w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/m138-t4.png 838w\" sizes=\"auto, (max-width: 763px) 100vw, 763px\" \/><figcaption class=\"wp-element-caption\"><em>M-138-T4 cipher device &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<p class=\"wp-block-paragraph\">M-138-T4 was further refined by the Navy and, as the M-138, was approved in August 1934 and became the first strip cipher used by the U.S. Army. The first units were ordered in January 1935.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\"><\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong><span style=\"text-decoration: underline;\">The M-138-A<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<p class=\"wp-block-paragraph\">Quickly problems were reported with the M-138 \u2014paper strips were getting stuck in the channels, due to the cylindrical shape of the rods creating the channels\u2014 and in November 1936 work was started on modifications.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The new version, M-138-A, was tested in 1938 and production started in 1939.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In 1942, as mass production was about to begin, a shortage of aluminium forced the Army to substitute the M-138-A.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">As the Navy had a plastic version of the M-138-A, the CSP-485, the Army purchased 5,000 units. These were found not practical, as the board warped in tropical climates.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<div style=\"height:110px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"651\" height=\"327\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-845p.png\" alt=\"\" class=\"wp-image-617\" style=\"width:auto;height:200px\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-845p.png 651w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-845p-300x151.png 300w\" sizes=\"auto, (max-width: 651px) 100vw, 651px\" \/><figcaption class=\"wp-element-caption\"><em>CSP-845 (plastic) &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<div class=\"wp-block-columns alignwide is-layout-flex wp-container-core-columns-is-layout-794e3cfa wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:60%\">\n<p class=\"wp-block-paragraph\">The Army thus had to send the existing aluminium devices (from the continental U.S.) overseas where the conditions were the worst, and made wooden versions, called SIGWOWO, for the continental U.S.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When the aluminium shortage ended production of metal devices could resume; all previous devices (M-138, M-138-A, SIGWOWO, plastic CSP-845) were declared obsolete, recalled, and replaced with metal CSP-845.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\">\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"878\" src=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-485-1024x878.png\" alt=\"\" class=\"wp-image-616\" style=\"width:auto;height:300px\" srcset=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-485-1024x878.png 1024w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-485-300x257.png 300w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-485-768x659.png 768w, http:\/\/sfisqlu.cluster100.hosting.ovh.net\/wp-content\/uploads\/2025\/03\/csp-485.png 1361w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>CSP-845 &#8211; National Cryptologic Museum<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n<p class=\"has-text-align-left wp-block-paragraph\"><em>(For a broader history of strip and cylinder cipher devices, see <a href=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/index.php\/m-94\/history\/\" data-type=\"page\" data-id=\"108\">M-94\/History<\/a>)<\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Genesis of the M-138 In the 1920 and early 1930s, the field cipher device widely used by the U.S. Army was the M-94. However, its alphabets were stamped on aluminium discs which could not readily be replaced. Late in 1933 the Army, recognizing the added security of being able to easily change alphabets, devised plans [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":582,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"wp-custom-template-m-138","meta":{"footnotes":""},"class_list":["post-604","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>M-138 | History<\/title>\n<meta name=\"description\" content=\"In the 1920 and early 1930s, the field cipher device widely used by the U.S. Army was the M-94.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"http:\/\/sfisqlu.cluster100.hosting.ovh.net\/index.php\/m-138\/history\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" 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