On a submarine, the mast plays various crucial roles. The snorkel ensures that the submarine can intake air during submerged navigation, radar antennas are used for actively searching surface targets, and the attack periscope observes targets underwater using optical principles. The multifunction mast integrates electronic reconnaissance, suppression, and radar search functions. So, what are the differences between the attack periscope and the electro-optical mast? Why is the electro-optical mast more flexible? Lastly, why do modern submarines still need to retain traditional periscopes rather than relying entirely on electro-optical masts? What is the logic behind this design? Various mast-like devices on submarines serve distinct purposes. Firstly, the snorkel is essential for both nuclear-powered and conventional submarines, facilitating gas exchange during submerged navigation. Next is the radar antenna, which, like traditional radar, emits and receives electromagnetic waves to actively detect enemy targets on the surface. Then comes the attack periscope, which uses optical principles to refract surface imagery underwater, akin to a camera with an optical viewfinder, equipped with a complete fire control system for sea attacks. The multifunction mast is a system that integrates electronic reconnaissance, electronic suppression, and radar search functions. The electronic support mast is mainly responsible for passively receiving electromagnetic signals from the surface to determine the coordinates of radiation sources. The power mast provides necessary electrical power to the submarine. Additionally, communication antennas and reconnaissance antennas are responsible for communication liaison and gathering intelligence information, respectively. Electro-optical masts are divided into attack and search types; the former is mainly used for sea attacks, while the latter is used for sea and air searches, including navigation tasks. The attack-type electro-optical mast can be seen as a high-tech "mirrorless" camera, replacing traditional optical sights with screens and cameras, enabling operators to directly view images captured by the camera, simplifying interaction with fire control and search systems. The search-type electro-optical mast requires a larger pitch angle to detect targets such as aircraft in the sky. In summary, although both the attack periscope and attack-type electro-optical mast are used for sea attacks, they differ in technology and usage. The periscope relies on optical equipment to transmit images, while the electro-optical mast presents real-time images directly through cameras, and the latter typically has higher technological content and more complex functions. Regarding the question of single-lens reflex cameras and mirrorless cameras? In fact, the attack periscope uses optical refraction technology. A basic periscope can be composed of a vertical pipe and two plane mirrors set at a 45-degree angle. When the upper part of the periscope is aimed at the target, the lower mirror reflects the image of the target, allowing the observer to see it. However, the design of periscopes on military submarines is more complex. As early as 1906, optical periscopes were invented and widely used during World War II, based on mirror-reflection observation technology. However, such systems have several problems: Firstly, traditional periscopes need to extend from the top to the bottom of the submarine's conning tower, limiting the layout of the hull structure and internal space. Secondly, it allows only one person to observe at a time, usually the captain alone, leading to insufficiently timely information transmission. Thirdly, installing periscopes requires openings in the pressure hull of the submarine, which poses a challenge to the structural strength and sealing of the submarine.