One aspect of this lightness business that seems to continually be overlooked is that once an engineering problem is solved, creating a wider envelope, then that envelope will be exploited.
For example IMI working with Oto Melara developed the 60 mm HVMS round in the 80s to bring the 60 mm gun, which could be carried by an M113 up to the same lethality as the standard 105s of the day. They succeeded. An M113 with a 60 mm HVMS could outrange a T55. IMI then went on to apply what they had learned on the 60 mm to their 90, 105 and 120 mm rounds making them more lethal and once again an M113 with a 60 mm HVMS was exceptionally vulnerable.
Likewise, as people develop lighter, more effective armours allowing for 20 to 30 tonne vehicles to be introduced, and let's stipulate that some magic wand is waved and they achieve the protection levels of the current M1A2 TUSK, some bright spark is going to suggest applying 60 tonnes of that stuff to the M1A2 running gear so that it is invulnerable to an even greater range of threats (promptly to be countered by someone with a man-portable chemically powered laser or some such).
The US and everybody else knows how to get 60 tonne vehicles into theater and support them there. It is only going to get easier in the future (snap on armour, hybrid engines, chemically powered electro-magnetic rail guns etc.) If it can be done, it will be done. It may take three aircraft (vehicle, armour and crew with ammunition and supplies), or it may be done by prepositioning or by airship or high speed ships. I dunno.
But it can be done, therefore it will be done.
The only question is how much is it going to cost the enemy to defeat a 20 tonne, 30 tonne, 40 tonne or 60 tonne tank and how big a launcher do they have to bring up to destroy the vehicle. The more expensive the weapon, the fewer you are likely to encounter. The bigger the weapon the easier it will be to find and to counter.
I'm with a_majoor on this one, to an extent (there is still a place for classifying forces according to deployability of the platforms and designing accordingly), but given that it is relatively easy to transport extremely massive systems by sea it only makes sense that if sea-lift is to be supplied it should be as flexible as possible.
PS flexibility is not enhanced by grafting on entirely unrelated functions - such as supporting a land force (which requires a vessel to stay in place) vs supporting a naval force (which requires a vessel to move).
) seems to be the only way to get them off of Canada's shores in any meaningful number.
