The KDY bridge tower is a distinctive element used across a vast number of KDY-originated starship classes. Its known properties allow new ships to be immediately scaled, although the towers are often very different in detail. They are a distinctive feature of Imperial Star Destroyers and many other ships in the Imperial Starfleet.
The basic KDY bridge tower consists of a neck of varying height (sometimes so short as to be invisible) lifting a hexagonal 'bridge' above the dorsal superstructure. The upper surface of these towers almost always feature a pair of geometric spheres at either side and an H-shaped structure located centrally. The actual primary bridge - where the ship in question is usually commanded - is located centrally on the forward face of this hexagonal structure. The ship in question usually has auxiliary bridges in other locations.
The geometric globes atop KDY bridge towers have been the subject of controversy in the past. A scene in Star Wars: Return of the Jedi seems to indicate that they are the bridge's shield generators, and that destroying them will take down the shields around the bridge tower. However, according to the Incredible Cross Sections books and other sources, the domes actually house sensor equipment; the destruction of the domes in ROTJ in fact happened as a result of the shields failing under Rebel bombardment, rather than the destruction of the domes causing the shield failure. Nonetheless, the issue has not been helped by the fact that virtually all Star Wars video games have the domes as shield generators, and ludicrously make it possible to completely destroy a Star Destroyer simply by taking out the domes, then attacking the bridge.
This structure (either raised or lowered, on different classes) is a part of the starship's FTL sensor system