Prime Minister Lee Hsien Loong has sent valedictory letters to three retiring ministers, Mr Lim Hng Kiang, Mr Lim Swee Say and Dr Yaacob Ibrahim, lauding them for their contributions to Singapore over decades of service.

Among the third-generation ministers, he has known Mr Lim Hng Kiang, 64, for the longest time - since they were students at Cambridge University, the Prime Minister noted.

In the letter to the outgoing Minister for Trade and Industry (Trade), Mr Lee described Mr Lim Hng Kiang's approach to work as "hard-headed and practical, yet infused with a human touch".

"You are steady under pressure, analyse problems rationally and objectively, and have a sensitive feel for political considerations," Mr Lee wrote to the man who is leaving the Ministry of Trade and Industry (MTI) after 14 years at the helm.

He added: "I and my colleagues will miss your pragmatic, far-sighted approach to issues and your wise counsel in Cabinet."

As MTI chief, Mr Lim Hng Kiang built up key industry clusters in manufacturing, including petrochemicals, semiconductors and life sciences, Mr Lee noted. He and his team also negotiated an extensive network of free-trade and partnership agreements for Singapore. When the financial crisis hit in 2008, "your calmness and experience were pillars of strength", Mr Lee wrote.

In his letter to Mr Lim Swee Say, 63, Mr Lee recalled how the outgoing Manpower Minister struck him as a "determined, passionate leader who delivered results". He wrote: "You had a warm, down-to-earth personality. On the ground, you were practical, persuasive and effective."

Among Mr Lim Swee Say's career highlights, Mr Lee pointed to the introduction of Newater, where the challenge "was not the science or engineering", but how to persuade Singaporeans to accept the idea of recycling and consuming used water.

"This you achieved brilliantly," he wrote to Mr Lim Swee Say, who was then Environment Minister, saying people's acceptance of Newater has helped Singapore "substantially overcome a strategic vulnerability that has obsessed us ever since independence".

Mr Lee noted that as Manpower Minister, Mr Lim Swee Say had a strong understanding of the labour market and how to balance the interests of workers with the needs of businesses.

He praised Mr Lim Swee Say's ability to coin vivid catchphrases that have clung to Singapore's collective memory, such as "cheaper, better, faster" and "1/3 + 2/3 > 1" to describe the workforce composition of one-third foreigners and two-thirds locals.

"These were not idle wordplay or poor math, but embodied important economic and manpower realities and priorities in a form that Singaporeans could understand, remember and act upon," Mr Lee said.

In his letter to Dr Yaacob, 62, he highlighted the important role the outgoing Minister-in-charge of Muslim Affairs has played in helping the Government handle sensitive issues involving race and religion.

"I could rely on you to understand the national imperatives, present forthrightly the Malay/Muslim point of view and advise me candidly on how best to move forward with the support of the community," Mr Lee said.

He also recalled Dr Yaacob saying, in one of his first parliamentary speeches as Acting Minister, that "one can be a good Muslim and a good citizen". "This set an important direction for Singapore Muslims," Mr Lee wrote. "You have worked hard to lead the community to look forward, to integrate with non-Muslim Singaporeans, and to adapt and change with the times."

Dr Yaacob,the outgoing Communications and Information Minister as well, also pushed for investment in infrastructure, so that Singapore today has one of the highest broadband speeds and Internet penetration rates in the world, while ensuring no one was left behind by the new technology.

The trio, who collectively have 66 years on the front bench, will retire from the Cabinet on Monday. Their retirement, part of a wider Cabinet reshuffle, will see more fourth-generation leaders take the lead in key government roles.

In a Facebook post yesterday, Mr Lee said all three have been invaluable members of his team, and will be deeply missed. "But I have to let them go, so as to renew the leadership team for Singapore."