The US Air Force flew an A-10 Thunderbolt II on an alternative fuel last week. The fuel was a 50/50 mix of standard JP-8 fuel and a biomass-derived jet fuel blend. The effort is one of several to fly a variety of US military aircraft on synthetic and alternative fuels.
Replacing or augmenting military fuel supplies is far more complex than just “seeing if it works.” Long test programs are often necessary to analyze the performance loss (if any), maintenance costs (due to increased seal wear), and to quantify the other characteristics of the fuel blend. Notably, the fuel is not necessarily cheaper than normal fuel, so for the time being, at least, alternative fuels like this are not inherently a cost-saving measure.
Often, too, the original source for the alternative fuel base is still foreign, purportedly due to US government restrictions and limitations on creating new biofuel capabilities in the US. So while one goal may be to reduce the reliance on foreign oil, it might merely temporarily move the dependence to reliance on foreign biofuel.