From an engineering perspective the P38 was a semi-automatic pistol design that introduced technical features that are found in other semi-automatic pistols like the Beretta 92 and its M9 sub-variant adopted by the United States military.

The P38 was the first locked-breech pistol to use a double-action/single-action (DA/SA) trigger (the earlier double-action PPK was an unlocked blowback design, but the more powerful 9×19mm Parabellum round used in the P38 mandated a locked breech design).
The shooter could chamber a round, use the safety-decocking lever to safely lower the hammer without firing the round, and carry the weapon loaded.
 This lever can stay down, keeping the pistol "on safe" or be immediately returned to the straight position, keeping the weapon safely "ready" with a double-action trigger pull for the first shot.
Pulling the trigger cocks the hammer before firing the first shot with double-action operation.
The firing mechanism extracts and ejects the first spent round, cocks the hammer, and chambers a fresh round for single-action operation with each subsequent shot – all features found in many modern day handguns.
Besides a DA/SA trigger design similar to that of the earlier Walther PPKs the P38 features a visible and tactile loaded chamber indicator in the form of a metal rod that protrudes out of the top rear end of the slide when a round is present in the chamber.

The moving-barrel design mechanism operates by use of a wedge-shaped falling locking block underneath the breech.
When the pistol is fired both the barrel and slide recoil for a short distance together, where the locking block drives down, disengaging the slide and arresting further rearward movement of the barrel.
The slide however continues its rearward movement on the frame, ejecting the spent case and cocking the hammer before reaching the end of travel.
Two return springs located on either side of the frame and below the slide, having been compressed by the slide's rearward movement, drive the slide forward, stripping a new round from the magazine, driving it into the breech and, in the process, re-engaging the barrel; ending its return travel with a fresh round chambered, hammer cocked and ready to repeat the process.

The falling locking block design provides good accuracy due to the in-line travel of the barrel and slide.

Initial production P38 pistols were fitted with walnut grips, but these were later supplanted by Bakelite grips.

Sheet metal grips were used for a time on pistols produced in France after the war, being called "Gray Ghosts" by collectors on the account of their distinctive parkerizing and sheet metal grips.
Post war P1 grips were made of black colored plastic.
From an engineering perspective the P38 was a semi-automatic pistol design that introduced technical features that are found in other semi-automatic pistols like the Beretta 92 and its M9 sub-variant adopted by the United States military.
The P38 was the first locked-breech pistol to use a double-action/single-action (DA/SA) trigger (the earlier double-action PPK was an unlocked blowback design, but the more powerful 9×19mm Parabellum round used in the P38 mandated a locked breech design). The shooter could chamber a round, use the safety-decocking lever to safely lower the hammer without firing the round, and carry the weapon loaded.  This lever can stay down, keeping the pistol "on safe" or be immediately returned to the straight position, keeping the weapon safely "ready" with a double-action trigger pull for the first shot. Pulling the trigger cocks the hammer before firing the first shot with double-action operation. The firing mechanism extracts and ejects the first spent round, cocks the hammer, and chambers a fresh round for single-action operation with each subsequent shot – all features found in many modern day handguns. Besides a DA/SA trigger design similar to that of the earlier Walther PPKs the P38 features a visible and tactile loaded chamber indicator in the form of a metal rod that protrudes out of the top rear end of the slide when a round is present in the chamber.
The moving-barrel design mechanism operates by use of a wedge-shaped falling locking block underneath the breech. When the pistol is fired both the barrel and slide recoil for a short distance together, where the locking block drives down, disengaging the slide and arresting further rearward movement of the barrel. The slide however continues its rearward movement on the frame, ejecting the spent case and cocking the hammer before reaching the end of travel. Two return springs located on either side of the frame and below the slide, having been compressed by the slide's rearward movement, drive the slide forward, stripping a new round from the magazine, driving it into the breech and, in the process, re-engaging the barrel; ending its return travel with a fresh round chambered, hammer cocked and ready to repeat the process. 
The falling locking block design provides good accuracy due to the in-line travel of the barrel and slide.
Initial production P38 pistols were fitted with walnut grips, but these were later supplanted by Bakelite grips.
Sheet metal grips were used for a time on pistols produced in France after the war, being called "Gray Ghosts" by collectors on the account of their distinctive parkerizing and sheet metal grips. Post war P1 grips were made of black colored plastic.
Walther P38