A battlecruiser is a type of warship that combines the speed of a cruiser with the firepower of a battleship. Designed for long-range engagements, battlecruisers typically have lighter armor than battleships, allowing them to move faster and engage enemies from a distance. They were primarily used in the early 20th century during naval warfare. The concept of the battlecruiser was popularized by the British Royal Navy, particularly with ships like the HMS Invincible. While effective in certain naval battles, their vulnerabilities were exposed during World War I, leading to a decline in their use as naval technology evolved.