The codename is ‘Operation Indian Ocean’. The mission is to strangle al-Shabab finances by capturing seaside towns under its control, such as Barawe. 

Authorities say the al-Qaeda-linked group uses the towns to imports weapons and trade. Al-Shabab is nothing without them, says the Somali president Hassan Sheikh Mohammed.

But this mission was never going to be a surprise dawn attack by Somali government forces and their African Union allies. If anything, it has been purposefully signposted: "We are coming, leave."

Indeed, the army has been moving towards rebel-held towns in the Lower and Middle Shabelle provinces for weeks - enough time for al-Shabab to relocate their fighters and weapons.

I have been with AU troops for several days in Jowhar, the capital of Middle Shabelle and a few kilometres from al-Shabab lines. We have, so far, seen more dust storms than battles.

Soldiers tell me al-Shabab are fighting with everything - the group recently broke the banks of the Shabelle river to flood the roads and render them impassable for the AU force's armoured vehicles.

This war will not be settled with a hammer blow. The winners will perhaps be those who can keep the money flowing, and al-Shabab knows this also.

The group has blockaded most of the towns its fighters lost earlier this year, cutting off supply routes for anyone left behind.

The cost of conflict

Al-Shabab wants to make it as costly as possible for the internationally community to finance the AU mission.

For now most of the captured towns are resupplied by air – a costly and complex option - but for how long that can be maintained remains to be seen.

As territory shifts from one set of hands to another, civilians as usual pay the heaviest price. The president has already blamed al-Shabab for exacerbating a drought by blocking trade and movement near areas it controls. 

Tons of food meant for those on the brink of starvation in the south is locked in warehouses in Mogadishu, the Somali capital.

Lower and Middle Shabelle is the country's "bread basket". Farms are been abandoned and refugees flee to major towns. They are the lucky ones.

Others brave the shelling and the gun battles as towns change hands.

For now everyone is preparing for a long, costly and bloody war – something Somalia doesn’t need and can’t afford after already more than two decades of it.

Follow Hamza on Twitter: @Hamza_Africa