Recently I purchased this Sinn 8820t. As part of the purchasing process I was able to dig up a lot of material on this watch. Most of this was in German, so I thought I'd paraphrase it here to document the watch's background in English too.

Before I start out, a hat-tip to the operator of @sinn8820t, who's been documenting dial variations diligently.

It seems there have been two main iterations: the 8820t, and the 8820. The main difference between the 8820t and 8820 are:
- 8820t: produced in 1980s, depth gauge on the rehaut, folded bracelet links, metal case back (top)
- 8820: produced in 1990s and 2000s, 1-12 scale on rehaut, solid bracelet links, sapphire case back (bottom)


The newer 8820 I won't further cover—not much special going on there. The 8820t, though, has some fascinating features and variations.

First off, this was the first titanium watch that Sinn ever produced. In the 1980s titanium was still somewhat of a rarity in watchmaking. The analog depth gauge on the rehaut is quite uncommon on dive watches, as it's complicated to allow some water to trigger the gauge while keeping it out of the movement. Finally, the 8820t's is equipped with an NSA spring bracelet, allowing the clasp to stretch out by means of coil springs:



According to Sinn brochures, the 8820t could be ordered with a leather strap or a titanium bracelet:



On Sinn's website archive I found this picture of an 8820t with a leather strap:


Now, of the 8820t no less than 4 different dial variations have been documented (credit to @Sinn8820t on all photos below):

First, there's the:
1) "straight S" (left), the S dips below the line of inn
2) "tilted S" (right), the S keeps in-line with inn and is tilted slightly upwards

I haven't been able to figure out how many of these two dial variations were produced, and Sinn wouldn't tell me when I inquired with them.

Then, there's the u-boat dials:
3) u-boat, red (top)
4) u-boat, yellow (bottom)



According to Sinn's own website in 2007, these u-boat dials were produced for the Asian market. On German-language forums I've read 200 pieces were produced , but don't know if this concerns the red and yellow versions separately or combined.

Ok, that's all I have. If anyone spots any errors or has additional information: please let me know!

 

Nice write-up! Is there any markings in the bracelet? It looks like a NSA patent,
they have used the spring loaded clasp since the 1960/70s

 

Thanks! You’re right, it’s an NSA stamped clasp. I’ll edit the post above and mention this.