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A reference used in Wikipedia's Apollo Command/Service Module article is CSM06 Command Module Overview pp 39-52.pdf. It includes (bottom of document page #43, 5th page of pdf):

Imact Attenuation:

During a water impact the CM deceleration force will vary from 12 to 40 G's, depending on the shape of the waves and the CM's rate of descent. A major portion of the energy (75 to 90 percent) is absorbed by the water and by deformation of the CM structure. The module's impact attenuation system reduces the forces acting on the crew to a tolerable level.

The impact attenuation system is part internal and part external. The external part consists of four crushable ribs (each about 4 inches thick and a foot in length) installed in the aft compartment. The ribs are made of bonded laminations of corrugated aluminum which absorb energy by collapsing upon themselves at impact. The main parachutes suspend the CM at such an angle that the ribs are the first point of the module that hits the water.

The internal portion of the system consists of eight struts which connect the crew couches to the CM structure. These struts (two each for the Y and Z axes and four for the X axis) absorb energy by deforming steel wire rings between an inner and an outer piston. The struts vary in length from 34 to 39 inches and have a diameter of about 2½ inches.

Question: What did the internal and external parts look like? Are there photos available? I'm especially interested in the "steel wire rings between an inner and an outer piston" of the inner section, as I can't envision what that is at all.

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The crushable ribs:

enter image description here

The struts:

enter image description here

Inside of the struts:

enter image description here

This document says

The cyclic strut utilizes cyclic material deformation concept of energy absorption by rolling ductile metal torus elements (bracelets) in friction between a concentric rod and cylinder. The force applied to the strut causes the bracelets to roll, absorbing energy.

Sources:

Apollo Operations Handbook BK-II, Volume 1, page 1-15

Apollo Spacecraft Familiarization Manual, page 3-41

As far as photos being available, the struts are in many photos. Here's one I took of the Apollo 14 Command Module at KSC in 2010. You can see one of the struts through the hatch.

enter image description here

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    $\begingroup$ I didn't expect to find a photo of the inside of the struts - and I didn't - but I thought maybe there was one of the ribs. But every single photo I found of the Command Module under construction shows the other side of the vehicle :( $\endgroup$ – Organic Marble Jun 24 '18 at 13:44

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