In assignments, which factor pertains to a Soldier's length of service?

The factor that pertains to a Soldier's length of service is time on station. This term typically refers to the duration that a Soldier has been assigned to a particular unit or location. It is often used in various personnel management and assignment processes to evaluate the overall experience and tenure of a Soldier within the Army.

Time on station is significant because it can influence considerations for assignments, promotions, and overall career progression. Soldiers with longer time on station may be prioritized for certain opportunities, given that their stability and experience can be valuable to units in terms of proficiency and leadership.

Deployment history, while important in assessing a Soldier's experience and operational readiness, does not directly relate to the length of service as it reflects past operational engagements rather than the time served in a unit. Security clearance is vital for determining a Soldier’s eligibility for access to classified information but is not indicative of their tenure. Likewise, medical board refers to a process concerning medical fitness and does not pertain to the duration of service. Therefore, time on station is the correct choice as it directly correlates with a Soldier's service length.