In this June 22, 2016 photo, Don Holman, an engineer at the U.S. Army Natick Soldier Research, Development and Engineering Center in Natick, Mass., opens the door to a refurbished shipping container where kale and other lettuces sprout. Holman is testing the idea of growing vegetables hydroponically in a shipping container that could be put on board a submarine to provide fresh vegetables to sailors. (AP Photo/Elise Amendola)