There's only two watch companies with such strong reputations for making tool watches that can make patina - evidence of a life lived with the purpose that a tool watch was designed for - attractive.  Namely, a Swiss company that starts with an "R" and...Seiko.
 
And this is one of those watches - a full-serviced steel gray-dialed MACV-SOG 1970 Seiko 6106-8100 here, with new-old stock USMIL nylon strap, exceptional vintage Waltham W.C.C. military compass, and MACV-SOG patch.  Separate from it's SOG heritage (or perhaps the reason SOG chose it?), Seiko debuted this watch in the late 1960s as its very first “Sport Diver.”
 
But what of the MACV-SOG moniker we’ve attached to this Seiko sport diver? 
 
As documented in an article we wrote for Watches of Espionage (WoE), we tracked down and spoke with respected SOG operator, Michael “Magnet” O’Byrne, and uncovered a SOG-issued Seiko previously unknown to the watch community - the late 1960’s Seiko 6106-8100 automatic sport diver.
 
As the likely only HUMINT-trained Case Officer in Military Assistance Command, Vietnam – Studies and Observations Group (MACV-SOG) - and later combat pilot - O’Byrne earned three Bronze Stars and five Purple Hearts during his Vietnam tours.  During our chats, he shared a wealth of previously unseen photographs, stories about his tours, and, of course, his time with his USMIL-issued Seiko.
 
Before we spoke with O’Byrne, WoE had outlined the three Seiko models known to have been worn by SOG forces: the Arabic numeral-dialed Seiko 6619 (first the 6119-8280, then the 6619-8060), 6119-8100, and 7005-8030 automatic divers.  But the evidence then, that the Seiko 6106 was issued to MACV-SOG forces, was decidedly sparse and single-thread – the Special Forces History Museum website run by Jason Hardy asserted O’Byrne had been issued the 6106 and provided several photographs of the watch as issued to him.  Those photographs were the starting point to unraveling the mystery – two of which revealed O’Byrne wearing a discernable 6106-8100.
 
MACV-SOG, a multi-service United States special operations unit conducting highly classified covert unconventional warfare operations during the 1960/70s Vietnam conflict in North Vietnam, Laos, and Cambodia, issued Seiko watches either directly via its Counter Insurgency Support Office (CISO, run by Conrad “Ben” Baker) or instructing the recon men to buy them on the open market.
 
In 1969, CISO issued a May 1968 Seiko 6106-8100 dive watch (serial number 852824) to Special Forces Green Beret soldier Michael O’Byrne before he departed for his first of two tours in Vietnam.  CISO was established on Okinawa in 1963 to supply clothing, weapons and equipment to Special Forces in Vietnam, to include MACV-SOG.
 
Upon arrival at the SOG’s Command and Control North (CCN) command, O’Byrne was wearing a USMIL-issued watch.  Not just any watch, but a Seiko, issued originally on a canvas (later replaced with a rubber) strap replete with Waltham W.C.C. compass.  One of O’Byrne’s responsibilities during missions into Laos was to surveil the Ho Chi Minh Viet Cong supply trail and place wiretaps along it to gather additional intelligence on enemy logistic movements and patterns of life.

O’Byrne told us he would wear his Seiko, “on every trip across the fence because it gave off very little light, just enough to read the time and the compass still worked.”  In late 1969, on his last patrol leading RT Rhode Island, the Seiko would play an integral role (albeit in a less than traditional sense) during an operation that would earn him his third Purple Heart.
 
During a fire fight after an ambush, his W.C.C. compass partially deflected North Vietnam grenade shrapnel from O’Byrne’s wrist, damaging the compass in the process and resulting in a dislocated shoulder, shrapnel embedded in a bicep, and a concussion.  He was left with a scar the size of a quarter on his wrist (still visible during our conversation).
 
Of note, ABC's The Rookie Sergeant Time Bradford (played abely by Eric Winter, @ebwinter on IG) wears one of these watches, sourced by DCVW for the show.  Given Bradford's USMIL Special Forces background and joint ops with CIA, the watch is a natural fit for his character.

This Seiko MACV-SOG 6106-8100 automatic comes on a new-old stock USMIL-issued nylon strap, and with vintage Waltham W.C.C.military compass, SOG patch, springbar tool, second nylon strap, and rugged travel case.