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Chief of staff (COS)


The Chief of Staff (COS) is a high-ranking military officer who serves as the senior-most advisor and assistant to a commanding officer, typically at the division or higher level. The COS is responsible for ensuring the smooth functioning of the command and coordinates between different departments and units to achieve the commander’s objectives. This role involves overseeing administration, planning, communication, and general management duties within the military organization.

Key Takeaways

  1. The Chief of Staff (COS) is a high-ranking officer in a military organization who serves as the primary advisor and assistant to the commanding officer, typically to coordinate and oversee various staff departments.
  2. As an essential part of the command structure, the COS is responsible for ensuring effective communication, coordination, and decision-making within the organization, as well as between the commanding officer and other entities such as higher commands, political authorities, or other military branches.
  3. While the specific functions and responsibilities of the COS may vary between countries and military branches, common duties include strategic planning, resource allocation, performance evaluation, and crisis management, providing invaluable support to the commanding officer to achieve the organization’s mission and objectives.


The military operations term “Chief of Staff (COS)” is important because it denotes a critical role in the command structure of a military organization.

The COS serves as the principal advisor to the commanding officer, responsible for ensuring effective communication, coordination, and execution of plans and policies within the unit.

This position plays a vital role in the decision-making process, as the COS assists the commander in formulating strategic objectives, managing personnel, and overseeing operational activities.

Additionally, the COS handles a wide array of administrative tasks, allowing the commanding officer to focus on overarching mission objectives.

In essence, the Chief of Staff’s role is crucial for maintaining organizational coherence, discipline, and the overall effectiveness of the military unit.


The purpose of the position of Chief of Staff (COS) in military operations extends beyond the conventional boundaries of administration and organization. As a principal advisor to the commanding officer, the COS plays an essential role in facilitating the execution of strategic and tactical plans by synchronizing efforts across different components of the military hierarchy.

This involves efficient delegation of duties, ensuring smooth communication among various departments, and offering expert guidance to help maintain a high level of preparedness, responsiveness, and effectiveness in confronting dynamic security challenges. In exercising their duties, the Chief of Staff employs their skills and knowledge to align the vision and goals of the commanding officer with the resources and capacities of the military unit, be it on a macro scale in safeguarding national interests or a micro level targeting specific missions.

The COS assumes a vital part in decision-making processes, presenting thorough situational analysis and generating finely-tuned operational insights. As the linchpin of military operations, the Chief of Staff acts as the backbone, supporting the coordination and functionality of the military structure, enabling its members to fulfill their objectives successfully, while staying consistent with the overall organizational strategy.

Examples of Chief of staff (COS)

General Mark Milley, United States Army: General Milley served as the 39th Chief of Staff of the United States Army from August 2015 to August

In this role, he was the highest-ranking uniformed officer and primary advisor to the Secretary of the Army on matters related to Army operations, personnel, and resources. As Chief of Staff, General Milley was responsible for the overall readiness of the Army and its combat capabilities to support the national defense strategy.

General Charles Krulak, United States Marine Corps: General Krulak served as the 31st Commandant of the Marine Corps and was the Chief of Staff to the Commandant between 1995 and

As COS, he was the principle military officer responsible for coordinating the operations of the Marine Corps and reporting directly to the Secretary of the Navy and the President of the United States. General Krulak’s leadership contributed to the modernization and preparedness of the Marine Corps as a global expeditionary force.

General Sir Nicholas Carter, British Army: General Sir Carter served as the Chief of the General Staff of the British Army from 2014 to 2018 and is currently serving as the Chief of the Defence Staff. As the COS, he was the professional head of the British Army and the principal military advisor to the Secretary of State for Defence and the Prime Minister of the United Kingdom. His tenure as Chief of Staff involved implementing a program of modernization and transformation to ensure the effectiveness of the British Army in a rapidly changing security environment.

FAQs: Chief of Staff (COS)

1. What is the role of a Chief of Staff (COS) in the military?

The Chief of Staff (COS) in the military is a senior-ranking officer who provides administrative, strategic, and operational support to the commanding officer. It is a crucial role that ensures the coordination and efficiency of the organization they serve.

2. How does the Chief of Staff (COS) differ from an Executive Officer (XO)?

While both the Chief of Staff (COS) and the Executive Officer (XO) serve as advisors to the commanding officer, the COS focuses mainly on strategic, operational, and administrative aspects, whereas the XO usually oversees day-to-day management, logistics, and personnel issues.

3. What are the key responsibilities of a Chief of Staff (COS)?

The key responsibilities of a Chief of Staff (COS) include advising the commanding officer, coordinating staff activities, developing strategic plans, overseeing communication and information flow, and ensuring that the organization’s resources are aligned with its objectives.

4. What are the qualifications for a Chief of Staff (COS) position?

The qualifications for a Chief of Staff (COS) position typically include extensive military service with leadership experience, a strong knowledge of military operations, planning, and administration, as well as excellent communication and interpersonal skills.

5. In which branches of the military can a Chief of Staff (COS) be found?

A Chief of Staff (COS) can be found in various branches of the military, including the Army, Navy, Air Force, and Marines. They may also serve in Joint Commands and National Defense Headquarters.

Related Military Operation Terms

  • Veterans Affairs (VA)
  • Executive Leadership
  • Strategic Planning
  • Healthcare Administration
  • Medical Staff Management

Sources for More Information