The underground entrance connects to other underground facilities at the base as well. A large underground component measures approximately 23,000 square meters. The July 4 imagery shows several ramps leading into this area, though April 2 imagery gives a better view of the full extent of the complex during its construction. The April imagery also shows the construction of a tunnel leading from this underground facility to the administrative buildings nearby. The tunnel is no longer visible in the more recent imagery.
Besides the large underground structure, several smaller tunnels and bunkers were built throughout the base. This type of construction is in line with known Chinese practices in hardening military bases. The underground structures allow for unobserved activity and offer protection to vehicles or facilities critical to the Chinese mission in Djibouti.
Of course, the main purpose of the mission is to support Chinese naval vessels operating in this part of the world. For that reason, it is notable that no dock has been constructed yet at the part of the base that touches the coast. Such a structure probably will be completed eventually and will give the base independent access to the sea, relieving it of its dependence on the commercial port in Djibouti.
Aside from the naval purpose of the base, the construction also indicates the facility's significant air role. The current tarmac and a row of eight hangars suggest that aircraft such as helicopters could be based there someday. However, it is unlikely that the facility will host fixed-wing aircraft, because at 400 meters the tarmac is much too short to accommodate fighter jets or even larger drones, such as those in the Chinese Wing Loong family.
As China prepares to open its first military base overseas, it is clear that Beijing is laying down the infrastructure to provide long-term support to naval vessels and some aircraft on the Horn of Africa, near one of the world's chokepoints for trade.