Tianjin 天津 ST2 Wuyi 五一 (Five One)

Model : Wuyi 五一
Manufacturer : Tianjin Watch Factory 天津手表厂
Year of Production: 1960(s)
Case Diameter : 
Weight w/o strap: g 
Movement Model : ST2A (18 jewels) 
Type : Hand Wind 

Tianjin Watch Factory's Wuyi watch is earlier than its Dongfeng and of course Sea-Gull watches. The wiki says as below:
Preparations began in 1957 for the establishment of the Tianjin WuYi Watch Factory, which was completed the following year. An all-new 17 jewel watch entered production, with the brand name WuYi (5-1 i.e. May Day). These watches were based on Swiss designs (FHF 25/28 series) and were of good quality. Today they are much sought-after by collectors. Later calibre ST-2A WuYi watches featured some detail enhancements including shockproofing and extra jewels. In 1962 the factory moved to a new site and was renamed Tianjin Watch Factory.
The name of the factory was then Tianjin Wuyi Watch Factory. This piece is  powered by the latest calibre, an improved 18 jewels version, equiped with shockproofing and antimagnetic features.

The logo on the dial is blended numbers of "5" and "1".  The same logo is also signed on the crown.

On the caseback are the words "ST-2A", "中国“ (China),”天津“ (Tianjin),”全钢“(all stainless steel),”防震“(anti-shock)and "防磁" (anti-magnetic).   It is said  that the caseback marked anti-magnetic is the last generation of Wuyi. (link here).

More pictures here:
1. The watch;
2. The dial;
3. The movement 1;
4. The movement 2;

My other watches from Tianjin Watch Factory;