branrot--The pistol you see in Walker, Texas Ranger is a P5 Compact.
357SIG--During the 1972 Olympics in Munich, Germany, Palestinian terrorists took hostage members of the Israeli wrestling team. The outcome was not good. Several hostages, or all( I can't recall ) were killed, as were most of the terrorists. As a result of this tragedy, the West German police set out to improve their weaponry, including their handguns. There were a series of tests that became known as the West German Police Pistol Trials.
At the time, the police were carrying Walther PP and PPk in .32 ACP. I believe Walther's first submissions to the trials in 1974 were the PP Super, chambered in 9x18 "police", and the P4, in 9mm.
Both these pistols were adopted by various West German police agencies. I think the P4( a slightly improved and strengthened P38 ) was adopted by the Border Police.
In the second round of trials in 1978, Walther submitted the P5, a further evolution of the P38/P4 design. Sig-Sauer and Heckler&Koch also sumbitted pistols. All three guns turned out to be such good pistols that they were all declared winners. It was decided to let individual agencies choose which of the three they adopted. The Sig-Sauer entry was adopted as the P6. This is the excellent and underrated Sig 225. The Heckler&Koch entry was adopted as the P7, a pistol that has developed, and IMO deserves, a cult following.
All three of these pistols are 8 shot 9mms.
The "doohickeys" on the side of the P5 are a takedown lever, and a combination decocker/slide release lever. The pistol was produced from '78 to '98.
The P5C that you see in Walker, Texas Ranger was produced by Walther in response to requests for a more compact version of this fine handgun. They were successful to a degree, but there's not much that can be done to the width of the slide, since the P5 series utilizes the falling block locking design of the P38. P5C production began in '88 or '89, and is still being produced, although the numbers imported into this country have been quite small. The P5C is something special, and I wouldn't part with mine for 3 times what I paid for it.
I hope this helps. If I've posted any incorrect info, please feel free to correct me, as this was done from memory.