Military communications in the context of "Naval flag signalling"

Cryptography, or cryptology (from Ancient Greek: κρυπτός, romanized: kryptós "hidden, secret"; and γράφειν graphein, "to write", or -λογία -logia, "study", respectively), is the practice and study of techniques for secure communication in the presence of adversarial behavior. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others. Core concepts related to information security (data confidentiality, data integrity, authentication and non-repudiation) are also central to cryptography. Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords and military communications.

Cryptography prior to the modern age was effectively synonymous with encryption, converting readable information (plaintext) to unintelligible nonsense text (ciphertext), which can only be read by reversing the process (decryption). The sender of an encrypted (coded) message shares the decryption (decoding) technique only with the intended recipients to preclude access from adversaries. The cryptography literature often uses the names "Alice" (or "A") for the sender, "Bob" (or "B") for the intended recipient, and "Eve" (or "E") for the eavesdropping adversary. Since the development of rotor cipher machines in World War I and the advent of computers in World War II, cryptography methods have become increasingly complex and their applications more varied.

The arms industry, also known as the defense (or defence) industry or military industry is a global industry which manufactures and sells weapons and other military technology to a variety of customers, including the armed forces of states and civilian individuals and organizations. Products of the arms industry include weapons, munitions, weapons platforms, communications systems, and other electronics, and related equipment. The arms industry also provides defense-related services, such as logistical and operational support. As a matter of policy, many governments of industrialized countries maintain or support a network of organizations, facilities, and resources to produce weapons and equipment for their military forces (and sometimes those of other countries). This is often referred to as a defense industrial base. Entities involved in arms production for military purposes vary widely, and include private sector commercial firms, state-owned enterprises and public sector organizations, and scientific and academic institutions. Such entities perform a wide variety of functions, including research and development, engineering, production, and servicing of military material, equipment, and facilities. The weapons they produce are often made, maintained, and stored in arsenals.

In some regions of the world, there is a substantial legal trade in firearms for use by individuals (commonly cited purposes include self-defense and hunting/sporting). Illegal small arms trade occurs in many countries and regions affected by political instability.

Military engineering is loosely defined as the art, science, and practice of designing and building military works and maintaining lines of military transport and military communications. Military engineers are also responsible for logistics behind military tactics. Military engineering is a predecessor of civil engineering, currently differs in its applications across disciplines and specialized work. In the 20th and 21st centuries, military engineering also includes CBRN defense and other engineering disciplines such as mechanical and electrical engineering techniques.

According to NATO, "military engineering is that engineer activity undertaken, regardless of component or service, to shape the physical operating environment. Military engineering incorporates support to maneuver and to the force as a whole, including military engineering functions such as engineer support to force protection, counter improvised explosive devices, environmental protection, engineer intelligence and military search. Military engineering does not encompass the activities undertaken by those 'engineers' who maintain, repair and operate vehicles, vessels, aircraft, weapon systems and equipment."

The United States Army Signal Corps (USASC) is a branch of the United States Army, responsible for creating and managing communications and information systems for the command and control of combined arms forces. It was established in 1860 by Major Albert J. Myer who played a significant role during the American Civil War. It initially manages portfolios and new technologies that are eventually transferred to other U.S. government entities. Such responsibilities included military intelligence, weather forecasting, and aviation.

An arrowhead or point is the usually sharpened and hardened tip of an arrow, which contributes a majority of the projectile mass and is responsible for impacting and penetrating a target, or sometimes for special purposes such as signaling.

The earliest arrowheads were made of stone and of organic materials; as human civilizations progressed, other alloy materials were used. Arrowheads are important archaeological artifacts; they are a subclass of projectile points. Modern enthusiasts still "produce over one million brand-new spear and arrow points per year".