The designation 138th Mixed Brigade does not correspond to a widely documented or independently verifiable entity in major encyclopedic sources. As a result, detailed information about its formation, operational history, leadership, or disposition is not available in the established historical record.
The term follows the naming convention used by the Spanish Republican Army during the Spanish Civil War (1936–1939), in which infantry units were organized as mixed brigades (Spanish: brigada mixta) and numbered sequentially. Consequently, a "138th Mixed Brigade" would plausibly refer to a unit that was part of this structure, likely created after the Army’s re‑organization in late 1936. However, specific archival references, contemporary reports, or scholarly works that confirm the existence, composition, or actions of a brigade bearing this exact number have not been identified.
In the absence of reliable sources, any further description of the brigade’s activities, commanders, or engagements would be speculative and therefore cannot be presented here.
