Texas is currently home to 15 military installations with an economic impact of around $150 billion. However, the military installations account for only $14 billion in federal payroll spending in Texas. In addition, there are currently more than 118,000 Texans on active duty status across all branches of the military. These are not insignificant figures.
However, it is important not to conflate the issues of military presence and political union. The United States maintains nearly 800 military bases in more than 70 countries and territories abroad. No one would argue that those 70 countries are in a political union with the United States due to the presence of a U.S. military base, nor would anyone argue that they should be. The presence of these military bases on foreign soil is solely about shared defense concerns and security interests. It does not imply any further political connection.
After a Texit, Texas may not share a government with the rest of the United States, but we will still share defense and national security concerns. International military cooperation has been a cornerstone of U.S. defense policy since the Second World War and, while it has been suggested that there should be some reforms, the underlying policy is unlikely to change, especially close to home.
It is, therefore, highly probable that Texas would enter into a mutual defense pact with the United States that includes joint use and operation of existing military bases and facilities in Texas or their full transfer to the Texas Military Department. As a part of any mutual defense pact, Texas will likely have to pledge to spend a set percentage of its GDP on national defense, much like the reforms proposed for NATO. In return, the United States should guarantee the availability of military arms and equipment for tariff-free purchase by manufacturers in the United States and vice versa. Texas should stipulate that the mutual defense pact should only extend to commonly agreed defense concerns.
Any mutual defense pact of this nature could set a transition period where things essentially stay as they are now, operating under a joint command until such time as the already established Texas Military Forces are at full readiness.