The Howe brothers' crew builds an all-terrain wheelchair for a veteran.

The Howe twins build a vehicle for a Hollywood film.

The team tests the Riptide with disastrous consequences.

The Howe twins present the amphibious tank to the Army.

Sneak peeks are revealed as show veterans prepare for the next challenge.

Twelve veteran survivalists take on the badlands of Colombia.

Hunger, thirst and distrust threaten to wreak havoc on several competitors.

The survivalists struggle to adapt to the environment and each other.

The remaining survivalists trek across the scorching savanna to find food.

Scarce resources force the survivalists to seek food in uncharted waters.

The dehydrated and protein-starved competitors compete for resources.

The survivalists struggle to find nourishment to survive extraction.

The groups begin the treacherous, 10-mile journey to the extraction point.

The survivors reunite to discuss the challenge and answer fan questions.

In a special one-hour preview, 12 Naked & Afraid veterans prepare for the most formidable survival challenge on the planet - surviving 40 days and 40 nights in the sun-scorched bush of South Africa.

12 survivalists enter a location marked by one principle: Banish the weak.