Irwin served through out WWII with
Company A, 47th Armored Field Artillery Battalion
1st under the command of the 5th ARMORED DIVISION
then under the command of the 2nd ARMORED DIVISION
..

..

Private First Class Chevron pay grade E6 during WWII
changed in 1955 to E3

"Chevron" is an architectural term denoting the rafters of a roof meeting an angle at the upper apex. The chevron in heraldry was employed as a badge of honor to mark the main supporters of the head of the clan or "top of the house" and it came to be used in various forms as an emblem of rank for knights and men-at-arms in feudal days. One legend is that the chevron was awarded to a knight to show he had taken part in capturing a castle, town, or other building, of which the chevron resembled the roofs. It is believed from this resulted its use as an insignia of grade by the military.

One overseas service bar is authorized for each 6-month period of active Federal service as a member of a U.S. Service outside CONUS, from 7 December 1941 until 2 September 1946, both dates inclusive. In computing overseas service, Alaska is considered outside CONUS. An overseas service bar is not authorized for a fraction of a 6-month period.

On the dress uniform
The enlisted U.S. Insignia is centered on the right collar.
The enlisted Artillery Insignia is centered left collar.
See: Web Page
..

The worsted red cord and tassel worn with the U.S. Army's dress light artillery shako is called an Airguillette. It is worn only when personnel are in dress uniform.