Task Force 116 (TF-116) was the “brown water navy” tasked with securing the Mekong Delta region (Southern Vietnam) during the Second Indochina War (Vietnam War). The Mekong Delta was a very swampy region with numerous small waterways, dense vegetation, and very busy shipping traffic, all factors helping the Viet Cong infiltrate undetected. TF-116’s patrols were part of the US Navy’s “Operation Game Warden”. The Brown Water Navy was equipped with very fast, heavily armed River Patrol Boats (PBR’s) to deny Viet Cong insurgents access to bases and supplies in the Mekong Delta. PBR boats also inserted and provided heavy fire support for Navy SEAL raids in the delta. Game Warden was considered a success due to the high kill ratio (40 Viet Cong KIA for every American KIA; source: Brown Water Black Berets by Thomas Cutler, 1988, page 205-206 [https://www.worldcat.org/title/brown-water-black-berets-coastal-and-riverine-warfare-in-vietnam/oclc/17299589]) and reports from Viet Cong defectors describing the effects of the operations, most notably more infrequent resupply and loss of freedom of movement.
For more information, see:
- https://www.mrfa.org/us-navy/us-navy-mobile-riverine-force/task-force-116/
- https://www.tf116.org/ (official veterans’ association, many excellent photos in the photo gallery)
The beret shown on this page belonged to Lt. Robert C. Blanchard, who was assigned to RIV PAT FLOT 5 as staff (source: https://books.google.com/books?id=cFTfH6Muw1YC&pg=PA127&lpg=PA127&dq=tf+116+robert+c+blanchard).
Patch:
The patch is made from bullion wire and covered by clear plastic. The plastic might have contributed to the slight corrosion of the bullion wire by trapping moisture.
Inside:
Label/Business Card:
Appears to be South Vietnamese manufactured (foil size label), but the manufacturer’s label was replaced by Lt. Blanchard’s business card.
Usage Photos:
From https://www.pinterest.com/pin/brown-water-black-berets–515802963553209680/. 
An Operation Game Warden sailor prepares to shoot a flaming arrow. The River Patrol Force also relied on flamethrowers and water cannon to destroy enemy positions on Mekong Delta riverbanks (U.S. Naval History and Heritage Command, from https://www.navytimes.com/news/your-navy/2019/12/15/arsenal-the-river-patrol-boat-was-the-backbone-of-the-brown-water-navy/).
The berets appear to be worn mainly for ceremonial purposes since they were probably not practical in the field.