When you can see them clearly, often tough to do in black & white photos, they appear to be for signal hoists as there are multiple lines reaching down to the signals platforms to the left and right of the bridge. Probably had other uses as well. Best shot I could find . . .
"The heavy cruisers HMS Berwick, Suffolk and Cumberland, of the 5th Cruiser Squadron, on the China Station in the 1930s [2200 x 1359]."
"Remember that famous photo on the left? “Wait for me, dad!”, 5-year-old Warren Bernard, breaking free from his mother's hands, ran to his father, Private Jack Bernard, 1940. Well, Jack survived the war and returned home in October 1945."
Radio antennas. You'll see something similar protruding from the flight deck in the Yorktown image I posted today.
The carried radio antennaes, weather gauge equipment, navigation lights, as well as the aforementioned halyards for signal flags.
"Crew of Austro-Hungarian Aviatik B.II demonstrating method of bombing from a plane, forward airfield Kolomea, Galicia (Eastern front) WW1, 1916 [Colorized] [1500 x 1085]."
Seriously OP... How dare you post this pic...And not give the story for the ship's boat by the aft stack - the one the sailor is painting. Why is it mocked up like a sailing vessel from the 1600s?
"28 February 1945 A group of M18 “Hellcat” tank destroyers - attached to the 6th Armored Division - halt before a German Mk VI King Tiger that they had just knocked out (unsure whether directly or abandoned by crew during the battle)." I see three Hellcats and the rest Shermans.
"[2918X1601] The last-ever Imperial Japanese fleet review with 98 ships present was dedicated to the 2600th anniversary of Emperor Jimmu’s enthronement. Off Yokosuka, October 11, 1940."
"Defiant Mark Is, including L7026, PS-V, and N1535, PS-A, of No. 264 Squadron RAF based at Kirton-in-Lindsey, Lincolnshire, in flight July 1940. (Photographer: B. J. Daventry. Colourisation - Nathan Howland)."