DAO hammer-fired pistols were briefly popular in LE during the Nineties, before striker-fired autos came to dominate. This is because the biggest problem with traditional double-action pistols as duty guns isn't two different trigger pulls, all "crunchenticker" conventional wisdom aside, but rather the fact that undertrained people will not decock the pistol by habit after shooting. Trying to stuff a cocked P226 or 92FS back into a Safariland gun bucket can cause unexpected loud noises.
The pictured pistol is a CS9D, the DAO variant of the CS9. It's uncommon enough that it's not even listed in the Standard Catalog of Smith & Wesson, 4th Edition. (Although the CS40D is listed. Perhaps unsurprising since the time this pistol was in the catalog coincided with the years that .40 caliber dominated the LE market.)
Another unusual feature on the DAO Chiefs Specials is that they are DAO by virtue of not having a single-action notch on the hammer. In other words, they are a true DAO, with re-strike capability and a full-weight, full-length trigger pull on each shot. The "DAO" 3rd Gen duty autos Smith sold at the time, like my 4046, had a trigger that was partially cocked by the slide and therefore did not have re-strike capability.
