Nevertheless, with some 4,000-5,000 personnel on the ground at any given time, the United States now has more troops in Africa than at any point since its Somalia intervention two decades ago according to Reuters. That ended in humiliation and withdrawal after the 1993 "Blackhawk Down" debacle in which 18 U.S. soldiers died.
The build-up of US military presence is due to seemingly two main reasons; al Qaeda and China. It wants to stem the tide of the rising influence of Islamic insurgency and other militant groups as well as win influence in a continent that could become an increasingly important destination for American trade and investment as China's presence grows in Africa.
Obama's week-long African tour will focus on military and security issues apart from food security and democracy. He is expected to douse fear that the US is militarising Africa for its own benefits shrouded in the war against terror. In the Horn of Africa, the vast majority of US forces deployed in Africa are at a major French military base in Djibouti, a tiny country sandwiched between northern Somalia, Ethiopia and Eritrea.
Experts reveal the military base has provided a staging post for occasional special forces deployments and drone and air attacks against Islamist militant targets in Somalia. However, US officials have refused to comment. The base was also allegedly instrumental for NATO's operations in Libya.
The US views its military presence in Africa as key in a continent where China is rapidly expanding and has surpassed the United States in terms of trade relations in Africa. China has huge investment in mining, energy and infrastructure and also a key ally of Sudan's President, Omar al Bashar which of course has always bolstered him against the West.
US officers believe its limited military missions have gone a long way in reducing initial African scepticism over Germany-based AFRICOM, set up in 2008 to bring all US military activities in Africa under one unified command, rather than dividing responsibility between commanders in Europe, the Middle East and Asia.
"We are focusing on building human capital," says Major General Charles Hooper, head of strategy and plans at AFRICOM. "The smaller missions can be some of the most effective when it comes to gaining trust."
In Angola, Namibia, Democratic Republic of Congo and elsewhere, US engineers have helped train local counterparts in landmine clearance. In southern Africa, military medics have helped local armies tackle HIV infection while in Mauritania, the focus has been on veterinary aid to local ranchers.
US warships combating piracy off both East and West Africa are increasingly frequent visitors to local ports. One US aim is to convince African militaries their interests are best served by remaining democratically accountable and not interfering in politics.
Some operations, however, have hit just that problem. The hunt in Central African Republic for Ugandan warlord and head of the rebel Lord's Resistance Army Joseph Kony has largely been suspended following a March coup in CAR.
The anti-LRA mission had been the only one in Africa in which combat troops were deployed, involving just over 100 US special forces personnel. US forces continue to train Ugandan and other armies as part of that operation.
Critics in Africa complain Washington's approach to the continent has become increasingly militarised and focused on counterterrorism. Others worry US military clout may ultimately be used to seize resources. Administration officials disagree and point to Obama's visit as evidence of US intentions.
"This trip ultimately disproves the notion that we're somehow securitising the relationship with Africa," Deputy National Security Adviser Ben Rhodes told a conference call last week. "This trip is expressly devoted to trade and investment, democratic institution-building, young people and unleashing economic growth through some of our development priority."
In general, US forces have only been able to operate when African governments - or sometimes France, which maintains a network of bases in former colonies - allow them to. Permission can be quickly withdrawn for political reasons. The United States still treads carefully in Somalia, the scene of a serious reverse in 1993 when militia fighters killed 18 Americans on a mission to capture a Somali warlord in support of a UN mission.
US officials say there are often one or two US liaison officers deployed inside Somalia helping African Union forces fight Islamist group al Shabaab - which is linked to al Qaeda - on behalf of Somalia's transitional government. Most of the US support for the African Union mission AMISOM remains outside the country, training forces in Kenya, Uganda and elsewhere.
It is a similar picture on the other side of the continent, where the US military is also acting primarily in support of local nations and France. The aftermath of the 2011 Libya war has seen a flood of weapons and militants across the Sahel, fueling the rise of al Qaeda in the Islamic Maghreb which briefly captured much of northern Mali before a French offensive there earlier this year.
The US Air Force provided much of the transport for both African and French reinforcements in Mali, while US air tankers from RAF Mildenhall in England have flown long missions over the Sahara refuelling French combat jets. Some 100 US personnel deployed to Niger to set up a drone base. Unlike in East Africa, however, the drones will be unarmed and used only for reconnaissance to track Islamist militants like Boko Haram in Nigeria.
The US and African officials say Washington has long been reluctant to share its most sophisticated intelligence with African partners, in part over worries it might fall into the wrong hands. African officers say that if they are to be truly effective at fighting militants in their own countries and as part of broader Mali-type missions, they need to know as much as possible about rebel movements, locations and plans.
"The Americans are our friends - but often they are friends who are not frank," says former Senegalese army chief Mansour Seck, also an ex-ambassador to Washington. "They have a tendency to ask you what you have but will not tell you what they have."
