What is a tactical penetration descent?
According to LOCAL FLYING OPERATING INSTRUCTION / 440 AIRLIFT WING INSTRUCTION 11-250 / OPR 440 OSS/OSA:


  5.7.4. ARRIVAL PROCEDURES:
  5.7.4.1. DESCENTS:
  5.7.4.1.1. TACTICAL (PENETRATION) DESCENT (Overhead, Downwind, Beam, etc): High rate (unrestricted) visual descent profile designed to transition an aircraft from a high-level altitude structure to a low-level altitude structure putting the aircraft in a safe position to execute a tactical approach.
  ...
  5.7.4.1.3. TACTICAL (PENETRATION) DESCENT ASSAULT – High rate (unrestricted) visual descent profile designed to transition an aircraft from a high-level altitude structure to a low-level altitude structure putting the aircraft in a safe position to execute a tactical approach to an assault landing zone. Note: A separate penetration descent profile may also be flown to Mackall AAF (HFF), see Pope Aircrew In-flight guide for procedures.
  5.7.4.1.3.1. Arrival Procedures:
  5.7.4.1.3.1.1. When sequenced, commence penetration descent to a tactical approach, ARA, or normal pattern. Request desired approach as early as possible upon switching to Pope Tower.
  5.7.4.1.3.1.2. Remain at or above 2500’ MSL until within 5 NM of Pope. Do not descend below 720’ MSL until given clearance to land from Pope Tower.


See also fooot's answer to another question, where he describes a tactical descent as an extremely steep descent, and a tactical approach as an extremely steep approach.

According to other sources, the technique in question might also be called (depending on the exact landing circumstances) an Assault Landing, a Sarajevo Approach or even a Khe Sanh Approach or an Overhead Approach.