Yes it's snk381 not the 800 series. MACV-SOC - Military Assistance Command, Vietnam – Studies and Observations Group. The soldiers used several series of seiko 5s when deployed in Vietnam. This snk381 looks the most similar to those used in Vietnam. https://www.watchesofespionage.com/blogs/woe-dispatch/vietnam-macv-sog-seikos-setting-the-record-straight
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