I will be discussing the use of ultrasonic nondestructive testing by  the military. "Defending the national interest requires the use of  sophisticated artillery, technologies and equipment. These defense  systems are subject to a high degree of stress whether they are missile  systems, or the jets and naval vessels that launch those systems. A flaw  or weak spot caused by corrosion or wear can cause a critical component  to fail and damage a serious investment. Nondestructive testing (NDT)  for the military and defense industry is an indispensable part of  fielding and maintaining these systems. Nondestructive testing for the  military is widespread and essential. It ranges from relatively  straightforward NDT such as ultrasonic testing of welds aboard naval  vessels to the testing of complex aerospace components that combine  metals and composite materials. In either case, the safety of the  sailors, soldiers, marines, and airmen who operate these systems depends  on regularly performed military NDT" (Nondestructive Testing for the  Military). 
      According to Military Nondestructive Testing,  various methods of nondestructive testing—ultrasonic, eddy current,  magnetic particle, radiographic, liquid penetrant, laser testing, and  leak testing—allow military personnel to inspect infrastructure,  vessels, vehicles, and weapons systems for flaws, corrosion, and other  defects which could lead to failure and endanger the lives of servicemen  and servicewomen (Safety Precautions). 
     Ultrasonic  nondestructive testing (NDT) is a method used to characterize the  internal volumes of materials. It works by propagating high-frequency  sound waves well above the range of human hearing throughout the  material. It can be used to detect flaws and discontinuities in metals,  composites, and other materials. "High-frequency sounds travel through a  uniform medium until they reach a discontinuity that reflects them  back—such as air or fluid at the other side of the material—or  incongruity in the matrix of the material. These reflected waves can be  resolved into visual images that allow an ultrasonic testing technician  to see flaws in the material, determine if corrosion is present, or  detect corrosion eroding the thickness of the material. Ultrasonic  testing works well for contiguous materials like metals, but not as well  for materials where discontinuities are part of their normal makeup  like wood, wood composites, or paper materials" (A Comprehensive Guide).
      Some types of ultrasonic nondestructive testing are: Straight Beam,  Angle Beam, Immersion Testing, Phased Array, Time of Flight Diffraction,  Total Focusing Method (TFM), and Guided Waves. (Please visit  https://www.zetec.com/resources/ultrasonic-testing-overview/ for a full  description of how each of these testing is done.

Douglas Norman
 

                                  References
Military and Defense Solution. Nondestructive Testing for the Military and Defense. N.D. 
   https://www.zetec.com/industries/military-defense-solutions/

Military Nondestructive Testing. Safety Precautions. N.D. 
      https://www.zetec.com/blog/military-nondestructive-testing-safety-precautions/#:~:text=The%20various%20methods%20of%20nondestructive%20testing%E2%80%94ultrasonic%2C%20eddy%20current%2C,and%20endanger%20the%20lives%20of%20servicemen%20and%20servicewomen.

Ultrasonic Testing Overview: A Comprehensive Guide to UT.  N.D.
     https://www.zetec.com/resources/ultrasonic-testing-overview/