coast defence ship: relatively small vessel sacrificed range and seaworthiness to carry weapons and/or armour powerful enough to take on the enemy's stongest ships when fighting in home waters. (taken from Conways: Steam, Steel and Shellfire)
calibre: the internal diameter of the bore of a gun, and consequently of the ammunition or shot fired from it. Barrel length was often quoted in 'calibres' (ie. 12"/45cal would be 45 x 12" long). (taken from Conways: Steam, Steel and Shellfire)
barbette: originally an open-topped armoured enclosure inside which was a gun mounting, usually on some kind of turntable, which fired over the top or the barbette wall. In the 1890s an armoured hood was added, the whole assembly coming to be called a turret. (taken from Conways: Steam, Steel and Shellfire)
S.M.S. stands for "Seiner Majestat Schiff" for German naval vessels.
Vertical markings on gun turrets (seen on Battleships/Battlecruisers c.1918) are deflection scales, indicating angle of train to other ships in her group.
Sometimes the picture on the postcard has been censored. Sometimes a bow wave has been painted on to give the appearance of a fast moving ship. Also, ship identification numbers on the side of ships could have been erased.
The three stripes painted on the bow turret of warships were painted during the Spanish civil war in 1937 as a recognition symbol of neutral warships.
Outlined on the warship below are booms and anti-torpedo nets attached to the side of a warship which would be extended out and the net would be lowered into the water on either side of the ship when the ship was anchored. These were commonly found on battlecruisers, battleships, and dreadnoughts in WWI. During the course of WWI the booms and nets were removed from the warships.
The structure built on top of the naval barrels on battleships/dreadnoughts or battlecruisers are launch rails for airplanes. This was an experiment to test if airplanes could be successfully launched off a turret of warship. The tests started at the end of the WWI and ended soon after.