A towed marine seismic source designed for shallow water sub-bottom geophysical surveys. It contains two independent chambers; the generator chamber releases a primary bubble of highly compressed air on command to generate an acoustic shock wave. The injector chamber injects air inside the bubble to ensure it collapses quickly, to reduce and suppress the sonic oscillation produced as the bubble collapses. This simplifies processing for the user by producing a clean acoustic signature. The GI-SOURCE 210 features a 105 cubic inch (ci) generator chamber and 105 ci injector chamber, giving a total volume of 210 ci. The air gun can be fitted with GI reducer inserts to reduce the generator bubble volume, for example allowing a reduced total volume of 150 ci (45 ci generator, 105 ci injector). It has a has a maximum operating pressure of 2000 psi. Multiple guns can also be configured in a cluster to increase energy output.