Angle Headed Flashlight TL-122D, MX-991/U

The classic TL-122-C angle-headed flashlight, widely issued and used during WW2. It was manufactured by the United States Electric Manufacturing Corporation under the USA LITE brand.

 Source : Here

There were four versions:

TL-122A.
Brass body flashlight in service before World War II. 
Painted olive drab with blackened metal screw caps over the lens and the base
TL-122B.
First plastic flashlight, OD color . Problems with early plastic formulation that smelled bad and had a waxy compound on the surface, issued September 1943
TL-122C.
Improved plastic, moisture proof design, issued April 1944.
TL-122D.
Extended base containing lens filters in blue/red/clear plus spare bulb. Issued late in 1944.

 Source : Here

The switch was dual function being either on/off or intermittent by pressing the small button for signalling purposes. For this purpose a selection of coloured gels is provided. The modern version of the TL-122 is essentially similar to its predecessor.

In Vietnam era an improved ABS body flashlight was introduced, the MX-99/U later upgraded to the MX-991/U. 

At some point a switch guard was added to the design.

These flashlights were similar to the TL-122D : 

Waterproof design

Metal slide switch with a button above the slider for Morse Code

Heat resistant,

Corrosion resistant

Belt clip on the back and a ring on the base.

A spare bulb and lenses, in two sections that join together with screw threads.

The flashlight is 8 inches long by 3 inches across the angle head.

The tube diameter is 1 3/4 inches.

The light is powered by two "D" cell batteries.

NEW desert tan MX-991/U right angle flashlights are currently being issued to US Navy and Marine aircrews flying over Iraq and Afghanistan . Made by Fulton and standard issue to US Naval flight crews.