Possibly prototype of removable plate bags that did not make it into the final Aircrew Endurance vest. Made of lighter weight (500D cordura?) Coyote Brown material. Has hand-written labeling like other modern prototype/test items (source: http://webbingbabel.blogspot.com/2016/08/prototype-sample-orc-industries-level-5.html). CMU-37 is for crew and CMU-38 is for (co)pilot (source: http://www.usmilitariaforum.com/forums/index.php?/topic/330974-cmu-37-and-38-prototype-body-armor-pouches/).
Arms on Backside:
It is unclear what these attach to since the platebags were not found with any other components.
Plate Bag Openings:
Final Aircrew Endurance Vest:
Image above from this article about the vest: https://www.navy.mil/submit/display.asp?story_id=78364