On April 6, 1917 The US entered WW1, and Amateur Radio was blacked out until Nov 1919.
World War I commenced in Europe in August 1914, and the US, under President Woodrow Wilson, was determined to remain neutral. As the fighting and the enemy’s resolve intensified, however, and Germany began sinking ships attempting to evade a naval blockade of England as well as non-military vessels, including the Lusitania with a loss of nearly 1,200 lives, it became inevitable that the US would enter the fray, and the leaders of the newly formed American Radio Relay League encouraged its 3,000 members to be prepared
The US officially declared war on Germany and Austria-Hungary on April 6, 1917, and the US government ordered most private radio stations in the US either to shut down or be taken over by the government. For the duration of WWI, it was against the law for private citizens to even own an operational radio transmitter or receiver, so amateur transmitting and receiving stations had to be disassembled. Amateur Radio operating privileges were not restored until November 1919 (QST resumed publication a few months earlier).
Once the US declared war, QST editorials urged qualified amateurs to volunteer their desperately needed skills to the military. Enlistees were particularly directed to the Navy, the nation’s principal service user of wireless. A specific program was developed to induct volunteer amateurs into the Naval Reserve for the duration — the Class 4 Naval Reserve. The requirements included citizenship, the ability to pass a physical examination, and the ability to send and receive Morse code at 10 WPM. Most volunteering radio amateurs chose to join this reserve, ARRL’s first Communications Manager Fred H. Schnell, 1MO, among them. He went to sea as a chief radioman.
ARRL co-founder Clarence D. Tuska received a commission as a lieutenant in the US Army Signal Corps, and he established a radio training school at Ellington Airfield near Houston, Texas.
QST itself suspended publication for the duration of the war. — Thanks to Mike Marinaro, WN1M, and United States Early Radio History by Thomas H. White.